JPS6240625A - Optical head - Google Patents

Abstract

PURPOSE:To make the titled optical head light in weight by raising the accuracy of a supporting member, and to drive easily the head by forming a member by which an optical system is supported, by a plastic formed body, and making a displacement sensor of its formed body and the corresponding part function as a target of the displacement sensor. CONSTITUTION:An optical beam from a laser diode 1 being a light source is made parallel by a collimator lens 2, applied to a polarizing prism 3 nd a transmitted light is made incident on a reflecting prism 4 and brought to a total reflection. This total reflected light is made to pass through a 1/4 wavelength plate 5 and led to an objective lens 7 which can be displaced in the optical axis direction and the tracking direction orthogonal to said direction by an actuator 6, and projected onto an optical disk in a shape of a spot. Said diode 1 is held by a laser diode holding frame 10, the lens 2 is held by a collimator lens holding frame 12, and the holding frame 12 is fixed to the holding frame 10. Also, the holding frame 10 and an optical head body 11 are formed as a solid plastic molding, a part corresponding to the prism 3 becomes a target, and the body 11 becomes light in weight.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical head for recording and reproducing information on and from optical recording media such as optical discs such as compact discs and video discs, and optical recording media such as magneto-optical discs. It is something.

[Conventional technology]

In a conventional optical head, a laser beam emitted from a light source consisting of a laser diode is projected as a spot onto an optical disk via an optical system including an objective lens, and the beam reflected by the optical disk is received again via the objective lens. There is one that leads to the element. In such an optical head, in order to accurately project the laser beam as a minute spot onto the information track of the optical disk, an actuator is provided to displace the objective lens in the direction of its tip axis to perform focusing control and to Tracking control is performed by displacing the information track in a direction substantially perpendicular to the information track. A typical actuator is configured to support a holder that supports an objective lens so as to be movable in the above-mentioned focusing direction and tracking direction, and to displace the holder in each direction by an electromagnetic drive means having a permanent magnet and a coil. For example, in Japanese Patent Application No. 59-170016, a holder for holding an objective lens is fixed to one end of two parallel plate springs arranged so as to be displaceable in the optical axis direction, and the other ends of these plate springs are attached to a relay member. and one end of two leaf springs arranged in a "V" shape so as to be displaceable in the tracking direction is fixed to this relay member.
The other ends of these leaf springs are fixed to a pair of posts provided on the base so as to extend in the optical axis direction, and a magnetic circuit including a permanent magnet and a yoke is attached to the base, and the magnetic flux passing through this magnetic circuit is An actuator is described in which a focusing coil and a tracking coil arranged transversely are fixed to an objective lens holder.

In addition, in information recording and reproducing devices using optical heads,
In order for the optical head to quickly access a desired information track, the carriage that supports the optical head is moved at high speed, for example, in the radial direction of the disk-shaped recording medium. During acceleration and deceleration of this movement, the objective lens is moved in the tracking direction. Undesired vibrations occur in the leaf springs that are supported in a displaceable manner, resulting in deterioration of positioning accuracy, loss of control, and long access times.

In order to eliminate such drawbacks, for example, Japanese Patent Laid-Open No. 58-
Publication No. 26331 discloses an optical head in which the amount of displacement of an objective lens is detected by a sensor and a tracking drive mechanism is operated according to the detected amount of displacement to prevent the above-mentioned unnecessary vibration. . In such conventional optical heads, the amount of displacement of the objective lens is measured using a capacitance type minute displacement detection sensor, an eddy current type minute displacement detection sensor, an optical minute displacement detection sensor, etc. It is fixed to a base, and its detection end is placed facing the side surface of an objective lens holder, and the holder is used as a sensor target. Therefore, the holder is made of cast metal such as zinc or aluminum.

On the other hand, in optical heads, objective lens It has been proposed that the holder be constructed from a plastic molded body.

[Problem that the invention seeks to solve]

In the optical head having the above-mentioned displacement sensor, if the objective lens holder is constructed from a plastic molded body, since plastic is generally an electrical insulator, a capacitance type sensor or an eddy current type sensor will not work. It will no longer be usable as is.

Further, optical sensors cannot be used as they are because plastic molded bodies are generally black and have a relatively low reflectance. Therefore, it is necessary to fix a metal plate such as an aluminum plate to the portion of the holder that faces the sensor. If a separate aluminum plate is used in this way, processing costs will increase and the weight will increase accordingly, which has the disadvantage that the significance of constructing an objective lens holder using a plastic molded body is considerably lost.

An object of the present invention is to eliminate the above-mentioned drawbacks, and to make it possible to use a sensor that can detect the position of the objective lens in a non-contact manner without using an additional member such as an aluminum plate, and in which the objective lens holder is made of plastic. The aim is to provide an optical head.

[Means for solving problems]

The present invention provides an optical head in which a displacement sensor detects the displacement of an optical system that irradiates a light beam emitted from a light source as a spot onto an optical recording medium as a displacement of a member that moves together with the optical system. In this method, a member that moves together with the optical system is made of a molded plastic body, and at least a portion of the molded plastic body facing the displacement sensor is configured to function as a target for the displacement sensor. It is characterized by the following structure.

[Function] In the present invention, a plating layer is provided on at least the part of the plastic molded body facing the displacement sensor, and this part is made of conductive plastic, so that a capacitive displacement sensor or a vortex The amount of displacement can be detected using a current type displacement sensor. Further, when a plating layer is provided, an optical displacement sensor can also be used since its reflectance is high. In this case, there is no need to provide a separate member such as an aluminum plate, so there is no increase in manufacturing cost or weight, and it can be manufactured at low cost, and the driving force of the actuator is small. .

〔Example〕

FIGS. 1A and 1B are a sectional view and a plan view showing an embodiment of the present invention. In this embodiment, a light beam emitted from a laser diode 1 constituting a light source is made into a parallel beam by a collimator lens 2 and is made incident on a polarizing prism 3 and transmitted through the polarizing film 3a, and the transmitted light is completely reflected by a reflecting prism 4. After being reflected, the light is guided through a 174-wavelength plate 5 to an objective lens 7 that can be displaced in the optical axis direction and a tracking direction perpendicular to the optical axis direction by an actuator 6, and is projected onto an optical disk (not shown) in the form of a spot.

In this embodiment, it is assumed that information recorded on an optical disc is to be reproduced. The reflected light from this optical disk follows the same optical path as the outgoing path up to the polarizing prism 3 and is incident on the polarizing film 3a, but on the returning path, the polarization direction is perpendicular to the polarizing direction of the outgoing path due to the action of the 174 wavelength plate 5. Therefore, all the returning light is reflected by the polarizing film 3a. The return light from the optical disk reflected by the polarizing film 3a is reflected by a critical angle prism 8 having a reflecting surface 8a set at an almost critical angle with respect to the central ray, as shown in a perspective view in FIG. The light is received by a photodetector 9 having a light receiving area divided into four parts,
Detecting information signals, focusing error signals and tracking error signals.

A laser diode 1 is held in a holding frame 10 and attached to an optical head main body 11. Collimator lens 2 is attached to holding frame 12
This holding frame 12 is positioned within the holding frame 10 for the laser diode and fixed by adhesive so that the light emitted from the collimator lens 2 becomes a parallel beam. Further, the polarizing prism 3 and the critical angle prism 8 are integrally configured so that the incident angle with respect to the center ray of the return light from the optical disk on the reflective surface 8a of the critical angle prism 8 can be adjusted.
It is rotatably held in the optical head main body 11. Further, the reflection prism 4 and the 174-wavelength plate 5 are integrally constructed and fixed to the optical head body 11, and the photodetector 9 is a holding member attached to the optical head body 11 facing the output surface of the critical angle prism 8. Attach it to 13. The entire optical head is formed into a box shape by the optical head main body 11 and the cover 14, and an opening 14a is formed in the portion of the cover 14 facing the objective lens 7.

In this embodiment, the laser diode holding frame 10 and the optical head main body 11 are constructed as an integrally formed plastic body, and the laser diode 1 is adhesively fixed to the holding frame 10 using an adhesive. Further, the collimator lens holding frame 12 is similarly made of plastic, and the collimator lens 2 is adhesively fixed with an adhesive, and the holding frame 12 holding the collimator lens 2 is placed inside the laser diode holding frame 10. The insertion position is determined so that the light beam emitted from the laser diode 1 via the collimator lens 2 becomes a parallel beam, and the laser diode is similarly adhesively fixed to the laser diode holding frame 10 using an adhesive.

Note that the holding frame 10, the optical head main body 11, and the holding frame 12
The plastic materials that make up are PC (polycarbonate) and PES (polyether sulfone).
, PP5 (poly phenyl sulfide), PEEK
(polyether, ether, ketone), epoxy resin, etc., or a mixture of these materials with fibers such as carbon fiber or glass fiber to increase strength can be used.

Next, the configuration of the actuator 6 shown in FIGS. 1A and 1B will be explained.

3, 4, and 5 are an exploded perspective view, a plan view, and a side view showing the actuator 6 in an enlarged manner. An objective lens 7 that irradiates a light spot onto a recording medium such as an optical disk is attached to a holder 21. This holder 21 is displaced in a focusing direction F parallel to the optical axis of the objective lens 7 to converge a light spot on the recording medium, and is also displaced in a tracking direction T perpendicular to the information track on the recording medium and the optical axis. , base 2 through the support mechanism to make the light spot follow the information track.
Connect to 3. This support mechanism includes a pair of focusing leaf springs 24a and 24b, and a middle 1! member 25;
A pair of focusing leaf springs 24a, including a pair of tracking leaf springs 26a and 26b.

Grooves 21a and 21b are formed at one end in the side wall of the holder 21 so as to extend in a direction perpendicular to the focusing direction F and the tracking direction T while facing each other parallel to each other when viewed in the focusing direction F.
upper and lower grooves 25 that are installed inside and have the other end opened in the relay member 25;
a and 25b.

Also, a pair of tracking leaf springs 26a and 26b
are left and right grooves formed at one end in the relay member 25 so as to extend in a direction substantially perpendicular to the focusing direction F and the tracking direction T while facing each other at a certain angle α in the tracking direction T. 25c and 25
d, and the other end is attached to grooves 27a and 28a formed in posts 27 and 28 provided on the base 23. This pair of tracking leaf springs 26a and 26b,
The distance between one end of the relay member 25 is shorter than the distance between the other ends of the posts 27 and 28, and the angle α formed by these leaf springs 26a and 26b is, for example, about 30°.
shall be.

Further, in order to drive the objective lens 7 in the focusing direction F and the tracking direction T, a pair of focusing coils 29a and 29b are fixed to the side surface of the holder 21 facing the tracking direction T, and a pair of focusing coils 29a and 29b are fixed to the outside of these focusing coils. Tracking coils 30a and 30b are integrally attached. These focusing coils 29a, 29b and tracking coil 30
A magnetic field generating member that generates a magnetic field in cooperation with a and 30b includes a pair of yokes 31 and 32 made of a magnetic material;
Outer yokes 31a and 31b on both sides of one yoke 310
permanent magnets 33a and 33b mounted inside along the outer yokes 32a and 32 on both sides of the other yoke 32;
Permanent magnet 34a installed inside along b
The yokes 31 and 32 are fixed to the base 23 so that their central inner yokes 31C and 32c are inserted into the focusing coils 29& and 29b, respectively.

In this embodiment, the objective lens holder 21 and the relay member 25 are made of plastic, and the base 2
3 and the posts 27 and 28 are made of integrally molded plastic. In this way, the objective lens 7, the focusing coils 29a, 29b, and one end of the focusing leaf springs 24a, 24b are each fixed to a predetermined location of the holder 21 with an adhesive, and the focusing leaf springs 24a, 24b are similarly fixed. The other end and one end of the tracking leaf springs 26a, 26b are each adhesively fixed to a predetermined location of the relay member 25, and the tracking leaf spring 26a.

The other end of the base 26b is adhesively fixed to a predetermined location of the boss 27, 28, and the base 23 is adhesively fixed to the optical head main body 11.

When the holder 21 and the relay member 25 that support the objective lens are constructed of plastic molded bodies in this way, the weight of the movable parts is significantly reduced, the control characteristics in the focusing direction and the tracking direction are improved, and the driving force is also reduced. Since it is small enough, permanent magnets 33a, 33b,
34a, 34b and the yokes 31, 32 can be made smaller, and the focusing coils 29a, 29b can be made smaller.
It is also possible to reduce the current flowing through the tracking coils aoa and 30b. Furthermore, since a plastic molded body can be manufactured at a lower cost than a metal molded body, the price of the entire optical head can be reduced.

In this embodiment, in order to detect the position of the objective lens 7 in the tracking direction T, a capacitive displacement sensor 36 is fixed to the side surface of the outer yoke 32a of one yoke 32 via a holding member 35. Further, a conductive metal plating layer 37 is formed on a portion of the objective lens holder 21 facing the displacement sensor 36, so that this portion functions as a target for the displacement sensor. Therefore, the position of the objective lens 7, that is, the holder 21 in the tracking direction T can be known by detecting the distance d between the plating layer 37 formed on the holder and the displacement sensor 36. In this way, by controlling the drive current supplied to the tracking coils 30a and 30b of the tracking drive mechanism based on the position signal detected by the displacement sensor 36, the optical head is moved at high speed and accessed to a desired information track. Undesirable vibrations can be prevented, and high-speed access is possible.

The present invention is not limited to the embodiments described above, but can be modified in many ways. For example, in the embodiments described above, a capacitance type displacement sensor is used as the displacement sensor, but an eddy current type displacement sensor can also be used. Furthermore, if the reflectance of the plating layer formed on the objective lens holder is high, an optical displacement sensor can also be used. Such an optical displacement sensor is a housing that is configured to project light emitted from a light source onto a plating layer via glass fibers, and to make the light reflected by the plating layer enter a light receiving element via glass fibers. Tonic Sensor (trade name) can be used. Furthermore, since the plating layer only needs to be formed at least on the portion facing the displacement sensor, it can also be formed on the entire surface of the holder.

Furthermore, when using a capacitance type or eddy current type displacement sensor, instead of providing a plating layer, the objective lens holder is made of plastic made conductive by mixing carbon, metal fiber, etc. into the resin. It can also be configured. Also,
The actuator for driving the objective lens in the focusing direction and the tracking direction is not limited to the one described above, and various types can be used.

Furthermore, there are various types of light sources, optical systems, and light receiving elements housed within the optical head body, and there are also various types of actuators. For example, a light source that emits three light beams can be used, and a photodetector that has a light receiving area divided into three or six parts can also be used. Furthermore, in the above example, the focusing error signal and the tracking error signal are detected using a critical angle prism having a reflective surface set at a critical angle. can also be detected.

〔Effect of the invention〕

According to the above-described optical head of the present invention, the member supporting the optical system including the objective lens is made of a plastic molded body, and at least the portion of the plastic molded body facing the displacement sensor is used as the displacement sensor. Since the support member is configured to function as a target, the support member can be formed at low cost and with high dimensional accuracy, and the support member can be made lightweight, making it easy and accurate to drive the support member.

Furthermore, high-speed access is possible by detecting the amount of displacement and performing tracking control. Furthermore, if the optical head main body and the holding frames for various optical systems are also made of plastic moldings as in the above embodiment, the entire optical head can be manufactured at a lower cost, and the optical head can be moved in the radial direction of the disk-shaped recording medium. The mechanism for driving the motor is also simple.

[Brief explanation of the drawing]

1A and 1B are a cross-sectional view and a plan view showing an embodiment of the present invention, FIG. 2 is a partial perspective view thereof, and FIG. 3 is an exploded perspective view showing an enlarged view of the actuator shown in FIGS. 1A and B. Figure 4 is a plan view, and Figure 5 is a side view. ■ Laser diode 2 Collimator lens 3 Polarizing prism 4 Reflecting prism 5 l/4 wave plate
6-actuator 7 objective lens 8 critical angle prism 9 photodetector 10 laser diode holding frame 11 optical head body 12 collimator lens holding frame 13 holding member 14- cover 21
Holder 21a, 21b Groove 23 Base 24a, 24b Focusing leaf spring 25
Relay member 25a to 25d groove 26a,
26b -) Racking plate springs 27, 28 Posts 27a, 28a Grooves 29a, 29b
Focusing coils 30a, 30b Tracking coils 31, 32--Yoke 33a, 33b, 34a, 34b--Permanent magnet 35
--- Displacement sensor support member 36 --- Displacement sensor 37 --- Plating layer patent
Applicant: Olympus Optical Industry Co., Ltd. Representative Patent Attorney: Hidetoshi Sugimura Patent Attorney: Oki Sugimura
Engraving of Figure 1 (No change in i゛, ) - Engraving of (No change in content) Figure 3 (Corrected figure) Figure 4, Figure 5 Procedures Correction September 1985 20th Japan Patent Office Commissioner Michibe Uga 1, Indication of the case 1985 Patent Application No. 179907 2, Name of the invention Optical head 3, Person making the amendment Relationship to the case Patent applicant ((L37) Olympus Optical Industry Co., Ltd. 4, Agent I, delete "It is black" on page 5, line 8 of the specification. 2. Delete "8 divisions or" on page 16, line 11 of the specification, and delete "8 divisions or" on page 16, line 15 of the same page. 8. In the drawing, 2nd rgJ and argJ are corrected as shown in the attached correction diagram.

Claims (1)

[Claims] 1. An optical head in which a displacement sensor detects the displacement of an optical system that irradiates a light beam emitted from a light source as a spot onto an optical recording medium as a displacement of a member that moves together with the optical system, A member that moves integrally with the optical system is made of a plastic molded body, and at least a portion of the plastic molded body that faces the displacement sensor is configured to function as a target for the displacement sensor. An optical head characterized by: