JPS6236744A - Optical pickup - Google Patents

Abstract

PURPOSE:To omit control jobs needed at assembling, etc., and to improve the workability by providing a mobile detecting part to an objective lens and forming an attachment part having a symmetrical distribution of magnetic flux density at the fixed yoke pat of an objective lens actuator holding said detecting part together with addition of a light emitting element and a photodetecting element. CONSTITUTION:An objective lens 34 is set between the 1st and 2nd fixed yokes 31a and 31b wound with tracking coils 33a and 33b. A position detecting member 44 is made of a plate material and contains a circular attachment part 45 and a slender detecting part 46 which is led out of a part of the part 45 and has its tip part bent rectangularly. Then the member 44 is set so that the part 46 is put at the center of the optical axis connecting a light emitting element 43 and a photodetecting element 40. At the same time, the part 45 is fitted to a lens holding frame 35. While the tracking current proportional to the output difference signal between the photodetecting quantities detected by the photodetecting areas 40a and 40b of the element 40 flows to both coils 33a and 33b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup used for recording and reproducing signals on an optical disc.

[Problems to be solved by the prior art and the invention 1 Conventionally, audio discs, video discs, data discs, etc.
Various pickups have been proposed for recording and reproducing signals on optical discs such as discs.

For example, there is one shown in FIG. This optical pickup detects a focus error signal using a critical phase method.

A light beam emitted from a light source 1 is collimated into a parallel beam by a collimating lens 2, and then enters a polarizing prism 3, is reflected by a polarizing film 4, and then reaches a reflecting surface 5. and,
The parallel light beam totally reflected in the right angle direction by this reflecting surface 5 is 17
The light passes through a four-wavelength plate 6, is focused by an objective lens 7, and is imaged onto an optical disk 8 as a light spot with a diameter of about one shoulder. The objective lens 7 is supported within an objective lens actuator 9 including a magneto, a yoke, a coil, etc. so as to be movable in two axes: the optical axis and the radial direction of the optical disk 80 perpendicular to the optical axis. Focus servo and tracking servo are performed so that the light spot is driven in the 21N1 direction and follows the center of the track of the optical disk 8 in a focused state. The light reflected from the light spot on the optical disk 8 is polarized It! Up to 34, the light follows the same optical path as the outgoing path, but on the returning path, the direction of polarization is perpendicular to the polarizing direction of the outgoing path due to the action of the 1/4 wavelength plate 6, so that it is transmitted through the polarizing film 4. The return light from the optical disk 8 that has passed through the polarizing film 4 is transmitted through the critical angle prism 1
0 and enters the photodetector 11. The critical angle prism 104 has an optical surface such that the angle of incidence of the return light from the optical disk 8 with respect to the optical axis is approximately the critical angle, and by reflecting the return light on this optical surface, the photodetector 11
It is input to.

The photodetector 11 has four light-receiving areas divided into two in the radial direction and tangential direction of the optical disc 8, and obtains data signals, focus error signals, and tracking error signals from the outputs of these light-receiving areas. It looks like this.

Incidentally, the present applicant has disclosed a conventional technique regarding an optical pickup having the above structure in, for example, Japanese Patent Laid-Open No. 55-146636.

By the way, the tracking servo mechanism of the objective lens actuator according to the above structure is configured such that the tracking error signal is fed back only during normal recording and reproducing operations. Therefore, during high-speed access, for example, when the pickup carriage is moved, a parallel force is generated in the driving direction of the carriage when the carriage accelerates or decelerates, causing unnecessary vibrations in the springs etc. that support the objective lens so that it can move in the tracking direction. Occur. This unnecessary vibration
Problems such as deterioration of positioning accuracy, disabling of servo control, and delay in opening during access have occurred.

In order to solve the above problems, etc., Japanese Patent Application Laid-Open No. 58-263
Publication No. 31 proposes a conventional technology regarding an optical head configured to detect the objective lens position using a capacitive non-contact minute displacement detection probe and to always perform closed-loop tracking control. . However, since this conventional technology uses an electrostatic receptacle type detection sensor, a linear ablizer is required to linearize the output signal, and the sensor diameter is large, making it difficult to make the optical pickup smaller and lighter. was not suitable for Furthermore, there is a possibility that the device may be affected by electromagnetic noise from the outside.

Furthermore, there is also a type of optical system that performs tracking control by rotating a mirror by a predetermined angle using an actuator, as disclosed in Japanese Patent Application Laid-Open No. 57-94942, which reflects a light beam from a light source toward an objective lens. In order to eliminate unnecessary vibrations generated in the mirror during high-speed access, the type pickup uses an angular position detection device to correct the tilt angle of the mirror during access.

However, it is necessary to leave a certain distance between the position detection light source provided in this prior art position detection device and the mirror. Furthermore, in order to detect the inclination angle of the mirror using the light flux from this light source, it is necessary to irradiate this mirror with a relatively large light spot, and when this light spot becomes large, the light receiving element that receives the reflected light has to receive the reflected light. The m region must also be made larger.

As a result, the overall size of the device has become larger and its structure has become more complex.

Therefore, the applicant of the present application filed an earlier application than the present application (Patent Application
Proposal for an optical pickup in which the position of the objective lens is detected by the objective lens actuator 7, and this detection signal can be used to prevent unnecessary vibrations of the objective lens during high-speed access etc. doing. The objective lens portion of this objective lens actuator is shown in FIGS. 8 and 9 (view from arrow C in FIG. 8).
First and second fixed yokes 13a and 13b made of a pair of magnetic materials are arranged parallel to the tracking direction T and are wound with tracking coils 12a and 12b, and both end sides of these fixed yokes 13a and 13b are arranged. A magnetic circuit is formed by connecting the first and second permanent magnets 14a, 14b to the tracking coils 12a, 12b.
An objective lens 15, which is movably supported by a spring or the like in the tracking direction T and is provided with a magnetic member, is disposed so as to face the lens. Then, one first fixed yoke 1
The light receiving element 17 is formed by forming a cutout such as a mounting hole 168 in 3a.
, and the light emitting element 18 is mounted by forming a cutout such as a similar mounting hole 16b on the other second fixed yoke 13b, and the detection part 1 is placed on the line connecting the light receiving element 17 and the light emitting element 18.
The position detection member 20 is inserted into the objective lens 15 so that the position detection member 9 is positioned.
It is fixed at

However, in such a structure, in order to mount the light receiving element 17 and the light emitting element 18, mounting holes 16a, 16b, etc. are formed in a portion of one of the first and second fixed yokes 13a, 13b near the first permanent magnet 14a side. Since the cutout was formed, the first and second portions centered around the objective lens 15
The magnetic flux density distribution became asymmetrical in the tracking direction T of the fixed yokes 13a and 13b. Therefore, it is necessary to adjust the position of the other second permanent magnet 14b so that the magnetic flux density distribution is symmetrical, and the space in the tracking direction T is reduced, resulting in a narrowing of the movable range of the objective lens 15. There was a problem.

The present invention has been made in view of the above circumstances, and even when a light receiving element, a light emitting element, etc. for detecting the displacement of the objective lens that occurs during high-speed access etc. is attached to a fixed yoke, the magnetic flux density distribution is not reflected by the objective lens. A fourth object of the present invention is to provide an optical pickup that can be made symmetrical in the tracking direction about the center, eliminate the need for permanent magnet position adjustment work, and improve workability.

Means and operation for solving problem E] In order to solve the above problems, the present invention provides an objective lens for irradiating the recording medium with light emitted from a light source, and also provides a means for irradiating the recording medium with the objective lens. In an optical pickup for recording and reproducing information, the optical pickup includes an objective lens actuator that controls the optical axis in at least one direction of the optical axis and a direction perpendicular to the optical axis. A detecting section is provided, and a mounting section with a symmetrical magnetic flux density distribution is formed on the fixed yoke portion of the objective lens actuator sandwiching the detecting section, and a light emitting element and a light receiving element are provided, thereby improving workability. That's what I do.

[Examples] Examples according to the present invention will be specifically described below with reference to the drawings.

1 to 7 relate to the first embodiment of the present invention, FIG. 1 is an explanatory diagram of the objective lens portion, FIG. 2 is a sectional view taken along the line A-A in FIG. 1, and FIG. 4 is a cross-sectional view of the objective lens actuator part of the optical pickup,
5 is a top view of FIG. 4, FIG. 6 is a perspective view of the position detection member, and FIG. 7 is a diagram explaining the principle of objective lens position detection.

In these figures, reference numeral 21 is an objective lens actuator 21 of an optical pickup. The outer frame 22 of this actuator 21 is formed into a cylindrical shape with both ends open. A permanent magnet 23 having a rectangular cross-sectional shape and an annular shape as a whole is fixed at approximately the center inside the outer frame 22. has been done. Further, on both pole sides of the permanent magnet 23, yokes 24a and 24b, which have a rectangular and L-shaped cross section and an annular shape as a whole, are fixedly provided. the yoke 24a,
A gap is formed between the yoke 24b and the yoke 24a.
, 24b and the permanent magnet 23 form a magnetic circuit. Further, a holding cylinder 25 is disposed within the outer frame 22. This holding cylinder 25 includes a substantially cylindrical middle cylinder part 25a with both ends open, and a coil holding cylinder part 25b which is integrally formed in a concentric cylinder shape on the outside of this middle cylinder part 25a and has one end (upper end side) open. It is formed from. Said coil holding cylinder part 2
A focusing voice coil 26 is wound around the outer periphery of the lens 5b. This focusing voice coil 2
The coil holding cylinder part 25b, around which the voice coil 26 is wound, has one end (upper) open side thereof inserted into and out of the gap formed by the yaws 24a and 24b so that the voice coil 26 faces the permanent magnet 23. has been done. The holding cylinder 25 has a spacer 27 disposed above the yoke 24a at the upper end of the middle cylinder part 25a. The outer frame 22 is supported by a focusing spiral spring 28a made of an elastic material whose periphery is held by the outer frame 22.
installed on. Further, the holding cylinder 25 is connected to the outer frame 22 by a focusing spiral spring 28a similar to that described above whose periphery is held by a spacer 29 disposed at the lower end side of the outer frame 22 at the lower end side of the middle cylinder part 25a. It has been installed with 1 knot. That is, the holding cylinder 25 is supported by the outer frame 22 so as to be freely displaceable in its axial direction (optical axis direction F) by focusing spiral springs 28a and 28b. A yoke holding frame 30 is attached to the inside of the outer frame 22 above the focusing spiral spring 28a, and this yoke holding frame 30
, a pair of first and second fixed yokes 31a, 3 formed in a bar shape and arranged parallel to the tracking direction T.
1b, and the first and second fixed yokes 31a and 31b.
A pair of first and second permanent magnets 3 connected to both ends of
2a.

32b is provided. Tracking coils 33a, 33b are wound approximately at the center of the first and second fixed yokes 31a, 31b. The first and second coils are wound with the tracking coils 33a and 33b.
An objective lens 34 is provided at the gates of the fixed yokes 31a and 31b.

The objective lens 34 is mounted in a lens holding frame 35 with its front axis directed toward the central axis of the outer frame 22. A magnetic member 36 is attached to the outside of the lens holding frame 35 and is formed so as to face the tracking coils 33a and 33b. The lens holding frame 35
A gap is formed between the magnetic member 36 and the tracking plate spring 37, which is a pair of elastic members that drive the objective lens 34 in the tracking direction T perpendicular to the optical axis. One end is inserted and fixed. The other end side of the tracking plate spring 37, 37 is inserted into the holding cylinder 25, and this holding cylinder 25
It is fixed inside the lower end of the. That is, the objective lens 34 is supported by the holding tube 25 via tracking leaf springs 37, 37, and is movable in the tracking direction T.

On the other hand, centering on the tracking coil 33a,
A pair of mounting holes 38 and 38' are bored in the first fixed yoke 318 portions located symmetrically with respect to the tracking direction T on both sides thereof as mounting portions for the light receiving element. The mounting holes 38 and 38'' are formed with the same cutout so that the magnetic flux density distribution in the tracking direction T centered on the objective lens 34 is symmetrical. An element fixing member 39 is attached,
A light receiving element 40 is fixed to this fixing member 39. This light receiving element 40 has light receiving regions 40a and 40b divided into two in the tracking direction T. In addition, a pair of mounting holes 41.4 are provided in the second fixed yoke 31b portion facing each of the mounting holes 38, 38' as a mounting portion for a light emitting element.
1' is drilled. The mounting holes 41, 41' are designed to form the same cutout so that the magnetic flux density distribution in the tracking direction T about the objective lens 34 is symmetrical. A light emitting element fixing member 42 is attached to a mounting hole 41 facing the light receiving element 40, and a light emitting element 43 is fixed to this fixing member 42. Further, a position detection member 44 is fixed to the lens holding frame 35 to which the objective lens 34 is attached. This position detection member 44 is formed of an annular mounting portion 45 made of a plate material or the like, and a detection portion 46 extending long and thin from a part of this mounting portion 45 and having an end thereof bent in a right angle direction. .

The position detection member 44 is arranged such that the detection part 46 is located at the center of the optical axis connecting the light emitting element 43 and the light receiving element 40, and the mounting part 45 is attached to the lens holding frame 35.
It is fitted and installed.

Note that a tracking current proportional to the output difference signal of the amount of light received detected by the light receiving areas 40a and 40b of the light receiving element 40 flows through the tracking coils 338 and 33b.

In such a configuration, when a focus error signal current is passed through the voice coil 26 during normal recording and reproduction, the holding cylinder 25
Force acts on the focusing spiral springs 28a and 28b.
Due to the deflection deformation, the objective lens 34 is displaced in the tracking direction F. Also, tracking error CfE M
When the current is applied to the tracking coils 33a and 33b, the objective lens 34 is similarly displaced in the tracking direction T due to the deflection deformation of the tracking leaf springs 37, 37.

Next, when the objective lens 34 moves 1° in the tracking direction due to a high-speed access operation, the position detection member 44 is displaced along with the movement, and the detection part 46 is emitted from the light emitting element 43 and sent to the light receiving element. Light 8 received by 40
Change the distribution. In the case where the objective lens 34 is not displaced, if the optical axis 43 of the light emitting element 43 and the center of the detection unit 46 are aligned with the dividing line in the tracking direction T of the light receiving element 40, the 2 The output voltage difference between the divided light receiving areas 40a and 40b is O. or,
When the objective lens 34 is displaced, the light receiving area 40 of the light receiving element 40 has a light intensity distribution proportional to the displacement of the detection unit 44.
The output voltage difference between a and 40b is proportional to the displacement of the objective lens 34 position. A servo system closed loop is formed by feed-punching so that a current proportional to this output voltage difference flows through the tracking coils 33a and 33b. At this time, the first and second fixed yokes 31a and 31b have a pair of symmetrical mounting holes 38° and 4, respectively.
1.41' is formed and the magnetic flux density distribution generated by the current flowing through the tracking coils 33a and 33b is in the tracking direction 1 with the objective lens 34 as the center.
becomes symmetrical with respect to Therefore, the magnetic force that moves the objective lens 34 in the tracking direction is generated appropriately in response to the displacement, and the objective lens 34 is held at the position of the displacement O to prevent unnecessary vibrations of the objective lens 34 that occur during high-speed access.

Therefore, the work of adjusting the position of the permanent magnet, etc. becomes unnecessary, and work efficiency is improved.

In addition, in the above embodiment, the first and second fixed yokes 3
18.31b with mounting holes 38.38- and 41.41'
However, in order to make the magnetic flux density distribution symmetrical in the tracking direction T with the optical axis of the objective lens 34 as the center, its shape may also be a round hole, a square hole, a cutout such as a groove, or an arbitrary shape for mounting. It is sufficient that a mounting part such as a protrusion is formed. Further, the detection part 46 of the position detection member 44 only needs to be fixed to a part that moves together with the objective lens 34, and can be formed integrally or separately, and its shape can be, for example, a light-shielding part that blocks light or a window part that transmits light. may be formed. Furthermore, the structure of the objective lens actuator is not limited to that of the embodiment.

[Effects of the Invention] As explained above, according to the present invention, the objective lens actuator of an optical pickup is provided with a fixed yoke around which a coil for driving the objective lens in the tracking direction is wound, and the magnetic flux density distribution is adjusted around the yoke. Since the mounting parts for the light-receiving element, light-emitting element, etc. for position detection are formed symmetrically around the objective lens, there is no need for adjustment work during assembly, etc., which has the effect of improving work efficiency. be.

[Brief explanation of drawings]

1 to 7 relate to the first embodiment of the present invention.
The figure is an explanatory diagram of the objective lens part, and Figure 2 is A-A of Figure 1.
Line sectional view, Figure 3 is a view taken from arrow 8 in Figure 1, Figure 4 is a sectional view of the objective lens actuator portion of the optical pickup, Figure 5 is a top view of Figure 4, and Figure 6 is a position detection diagram. 7 is an explanatory diagram of the principle of objective lens position detection, FIGS. 8 to 10 are related to a conventional example, FIG. 8 is an explanatory diagram of the objective lens part, and FIG. 9 is an explanatory diagram of the principle of objective lens position detection. FIG. 10 is a diagram explaining the principle of the optical pickup. 21...Objective lens actuators 31a, 31b...First and second fixed yokes 32a
, 32b...first and second permanent magnets 33a, 33b
...Tracking coil 34...Objective lens 38.38", 40.41'...Mounting hole 39...
Light-receiving element fixing member 40... Light-receiving element 42... Light-emitting element fixing member 43... Light-emitting element 44... Position detection member 45... Detection section Fig. 1 Fig. 2 41 31b Fig. 5 Figure 10 Figure 6 Gate Figure 8 Figure 7 □ Collection 9 Figure 1 o Entrance + 2b Procedural Ne1n Orthographic (spontaneous) September 20, 1985 1, Display of the case 1985 Patent Application No. 176692
Representative: Satoshi Shimoyama, Department 4, Agent: 160-5, Date of amendment order (self-motivated) 1. Specifications ■ On page 6, lines 11 and 12, ``earlier application, (patent application by Akiyumi Aki) )” has been amended to read “earlier application (Japanese Patent Application No. 175218/1982)”. 2. In the 9th and 10th lines of the 11th page for specifications, the words [Focusing spiral spring 28a] have been corrected to [Focusing spiral spring 28b]. that's all

Claims (3)

[Claims] (1) An objective lens actuator that is provided with an objective lens that irradiates the recording medium with light emitted from a light source, and that controls the objective lens in at least one direction of the optical axis or perpendicular to the optical axis with respect to the recording medium. In an optical pickup for recording and reproducing information, the objective lens is provided with a detection section that moves together with the objective lens, and a magnetic flux density distribution is created in the fixed yoke portion of the objective lens actuator that sandwiches the detection section. An optical pickup characterized in that a light-emitting element and a light-receiving element are provided by forming a symmetrical mounting part. (2) The optical pickup according to claim 1, wherein the mounting portion is a cutout portion formed symmetrically in the tracking direction with the objective lens as the center. (3) The optical pickup according to claim 1, wherein the mounting portion is a protrusion formed symmetrically in the tracking direction with respect to the objective lens.