JPH0526254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical head used for recording and reproducing signals on optical disks such as audio disks, video disks, and data disks.

Various types of optical heads have been proposed in the past, including one shown in FIG. 1, for example. This optical head is designed to detect a focus error signal using the critical angle method.

The linearly polarized light from the semiconductor laser 1 is converted into a parallel beam by the collimator lens 2 and sent to the polarizing prism 3.
After being reflected by the polarizing film 4 and totally reflected by the reflecting surface 5, it is converged by the objective lens 7 through the λ/4 plate 6 and onto the optical disk 8 with a diameter of approximately
The image is formed as a 1 μm light spot. The objective lens 7 is supported within an objective lens actuator 9 that includes a magnet, a yoke, a coil, etc., so as to be movable along two axes: the optical axis and the radial direction of the optical disk 8 perpendicular to the optical axis. The lens actuator 9 drives the lens in the two axial directions, and a focusing drive and a tracking drive are performed so that the optical spot follows the center of the track of the optical disk 8 in a focused state.

The reflected light from the optical disk 8 from the optical spot follows the same optical path as the outgoing path until it reaches the polarizing film 4, but on the return path, the direction of polarization is perpendicular to the polarization direction of the outgoing path due to the action of the λ/4 plate 6. It passes through the polarizing film 4. In FIG. 1, the return light from the optical disk 8 that passes through the polarizing film 4 is incident on the photodetector 11 via the critical angle prism 10. In FIG.

The critical angle prism 10 has two opposing optical surfaces 10a and 10 set so that the incident angle of the return light from the optical disk 8 with respect to the optical axis is approximately a critical angle.
b, and by reflecting the returned light three times in total on these optical surfaces, the focus error detection sensitivity is increased and the return light is made incident on the photodetector 11. Further, the photodetector 11 has four light receiving areas 11a to 11d that are divided into two in the radial direction and tangential direction of the optical disk 8, and receives data signals based on the outputs of these light receiving areas 11a to 11d.
A focus error signal and a radial error signal are obtained.

That is, in the optical head shown in FIG.
The return light from the optical surface 10 becomes a parallel light beam.
Since the angle of incidence with respect to a and 10b is approximately the critical angle for all the light rays, all the light rays are totally reflected and uniformly distributed to the four light receiving areas 11a to 11d of the photodetector 11, as shown in FIG. 2A. incident. On the other hand, if the optical disk 8 deviates from the in-focus position and the returned light incident on the critical angle prism 10 becomes convergent light as shown in FIG. 2B or divergent light as shown in FIG. 2C, the optical The angle of incidence of the returned light on the surfaces 10a and 10b is larger than the critical angle on one side and smaller than the critical angle on the other side, with the plane orthogonal to the plane of incidence passing through the optical axis as the boundary. Light and darkness occur in the tangential direction on the vessel 11.

The brightness and darkness in the tangential direction on the photodetector 11 is determined by the relationship between the incident angles of the light rays on both sides of the plane orthogonal to the plane of incidence passing through the optical axis of the returned light on the optical surfaces 10a and 10b. Since the contrast is reversed in the case of diverging light, the brightness and darkness are reversed in FIGS. 2B and C. Therefore, the light receiving areas 11a-1
Letting each output of 1d be a, b, c, and d, a focus error signal can be obtained by (a+b)-(c+d). Note that the radial error signal can be obtained by (a+c)-(b+d), and the data signal can be obtained by (a+b+c+d).

In the optical head shown in Fig. 1, the coil and permanent magnet are arranged below the objective lens 7, so when designing the optical path to the objective lens, there should be a gap between the coil and the permanent magnet that does not allow light to pass through. The optical path has to be formed through the optical fiber, which has the disadvantage that the structure becomes complicated and the assembly of the device becomes troublesome.

Also, Figures 6 and 7 of JP-A-56-119944
The figure shows a configuration in which a lens 65 is fixed to the upper surface of the block 56 facing the medium surface, a coil is fixed to the side surface of the block, and permanent magnets are arranged to sandwich the block. but,
In such a configuration, it is necessary to provide a cavity for forming an optical path inside the block, and the optical path must be formed through a gap in a member such as a coil or a permanent magnet that does not allow light to pass through, making the structure complicated. In addition, there is a drawback that assembling the device becomes troublesome.

Further, Japanese Patent Application Laid-open No. 117745/1983 discloses a structure in which a tracking coil and a focusing coil are fixed to a shaft, and a lens is fixed to the shaft via a support plate. However, in the case shown in Figure 6 of the above publication, the lens is placed quite far from the shaft, and in the case shown in Figure 9 of the above publication, a semiconductor laser and a photodetector are also placed near the lens, which reduces the weight around the lens. Because of the large size, the force generated in the coil is not accurately transmitted to the lens, which has the disadvantage that highly accurate tracking drive and focusing drive cannot be expected.

In addition, in the case of Figure 10 of the above publication, the lens is placed near the shaft as in Figure 9 of the above publication, but the optical axis of the lens is gradually tilted, which not only makes it impossible to perform accurate focusing control, but also causes aberrations. There is a drawback that tracking control and information signal reading cannot be performed accurately due to the occurrence of such problems.

The present invention eliminates the various drawbacks mentioned above, has a simple structure, is easy to assemble, is suitable for mass production, and is suitably configured to perform highly accurate tracking and focusing drives. The purpose is to provide a head.

In order to achieve the above object, the present invention irradiates a recording medium on which information is recorded in a track shape with a light beam from a light source as convergent light using a lens, and when reading the information using the reflected light, A first block for driving the lens in a first direction perpendicular to the medium surface without tilting the lens optical axis, the block having at least an upper surface facing the medium surface and a side surface perpendicular to the medium surface. 1 coil and a second coil for driving the lens in a second direction parallel to the plane of the medium and transverse to the information track, substantially fixed to at least the side surface, the first coil and the A second coil moves together with the block, and the lens is driven in the first direction and the second direction by the action of magnetic flux generated from a magnetic field generating means fixed to the base. In the optical head, the optical head has a through hole for passing a light beam, has a wall thickness smaller than a wall thickness of the block in the first direction, and is integrally formed with the block. A plate-like protrusion of a continuous member is arranged in the extending direction of the upper surface, and further surrounds the lens (a component around the lens that does not have a lens function). ) is placed and fixed on the upper surface of the plate-like protrusion around the through hole, and the length of the plate-like protrusion in the information track direction is set to be equal to or close to the external dimension of the peripheral part of the lens. and the magnetic field generating means is arranged at a position other than the space facing the plate-like protrusion in the first direction, with a gap between both the first and second coils. It is.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a perspective view showing the structure of an example of the essential parts of the optical head of the present invention. In this example, the linearly polarized light from the semiconductor laser 21 is transferred to the collimator lens 2.
2, the light beam enters the polarizing prism 23 as a parallel light beam and is transmitted through the polarizing film 24, and the transmitted light is totally reflected at right angles by the reflecting prism 25.
The elliptical beam is guided through a λ/4 plate 26 to an objective lens 27 such that the major axis direction thereof is in the tangential direction of an optical disk (not shown), and is projected onto the optical disk in a spot shape. The reflected light from the optical disk follows the same optical path as the outgoing path up to the polarizing prism 23 and enters the polarizing film 24, but on the returning path, the polarization direction is changed from the outgoing polarization direction due to the action of the λ/4 plate 26. Since the light beams are orthogonal to each other, all the returned light is reflected by the polarizing film 24. The return light from the optical disc reflected by the polarizing film 24 is reflected once by the optical surface 28a of the critical angle prism 28, and is divided into two parts each in the radial direction and tangential direction of the optical disc, as in the case of FIG. By making the light incident on the photodetector 29 having four light receiving areas 29a to 29d,
A data signal, a focus error signal and a radial error signal are obtained from the output of 9d in the same manner as explained in FIG.

The optical surface 28a of the critical angle prism 28 is set so that the angle of incidence of the return light from the optical disk with respect to the optical axis is approximately the critical angle, as in the case of FIG. In order to obtain the same detection sensitivity as the three-time reflection in the case of FIG. 1 by reflecting the returned light only once, a multilayer film is applied to the optical surface 28a as described in Japanese Patent Application Laid-open No. 57-122410. Apply anti-reflective coating. Further, the incident light to the critical angle prism 28 is P-polarized light, and the optical surface 28
The incidence plane on the polarizing film 24 of the polarizing prism 23 and the incidence plane on the optical surface 28a of the critical angle prism 28 are made to be perpendicular to each other so that the incidence plane with respect to a is in the tangential direction, and the temperature fluctuation of these incidence planes is In order to reduce deviations due to thermal expansion, contraction, etc., the polarizing prism 23 and the critical angle prism 28 are integrated by bonding or the like.

On the other hand, the objective lens 27 is held at one end of an arm 30 extending in a direction perpendicular to the optical axis thereof, and the other end of this arm 30 is placed on an extension of the optical path from the semiconductor laser 21 to the reflection prism 25. The objective lens actuator 31 is connected to the objective lens actuator 31. Here, the length of the arm 30 in the information track direction in FIG. 3 is drawn longer to make the optical system easier to see (see FIG. 4 for the exact length of the arm 30).

In this example, the objective lens actuator 31 is connected to the other end of the arm 30, and slides a bobbin around which a focusing coil 32 and a tracking coil 33 are wound in the optical axis direction of the objective lens 27. By bearing the shaft 34 rotatably within a plane perpendicular to the optical axis and generating magnetic flux in a direction perpendicular to the direction of the current flowing through the focusing coil 32 and the tracking coil 33, The objective lens 27 is linearly displaced in the optical axis direction via the bobbin and the arm 30, and also circularly displaced in a plane perpendicular to the optical axis, so that the optical spot follows the center of the track of the optical disk in a focused state. Focusing drive and tracking drive are performed so as to

4A and 4B are a sectional view and a plan view showing a specific structure of the optical head shown in FIG. 3. FIG.
The semiconductor laser 21 is held in an inner frame 41, and the inner frame 41 is fixed to an outer frame 42 with a spring 43 and a screw 44 so that the position of the inner frame 41 can be adjusted in the beam emission direction. This outer frame 42 is provided with an aperture 45 that narrows down the beam from the semiconductor laser 21 and also holds a collimator lens 22 that converts the beam into a parallel light beam, and this outer frame 42 is fixed to a substrate 46 with screws 47.

Further, the integrated polarizing prism 23 and critical angle prism 28 adjust the incident angle of the return light from the optical disk with respect to the optical axis on the optical surface 28a of the critical angle prism 28, as shown in FIGS. 5A and 5B. It is held by a rotating member 48 that is rotatably provided with respect to the substrate 46 so that the substrate 46 can be rotated. Further, the reflection prism 25 and the λ/4 plate 26 are integrated by adhesive or the like and fixed to the substrate 46, and the photodetector 29
is attached to the holding member 49 attached to the substrate 46 with screws 50, facing the exit surface of the critical angle prism 28.

On the other hand, a bobbin 51 that constitutes the objective lens actuator 31 and around which the focusing coil 32 and the tracking coil 33 are wound is formed integrally with the arm 30 that holds the objective lens 27. The bobbin 51 and the arm are rotatably supported by a shaft 34 installed on the substrate 46 via a fixed collar 57 and are slidably supported in the direction in which the shaft 34 extends, that is, in the optical axis direction of the objective lens 27. 30 integral structures are supported on the substrate 46 via elastic members 52 so that their displacement is not hindered.

Furthermore, a step is formed in the lens peripheral portion 70 around the objective lens 27 (a portion without lens action), and the lower surface 70a of this step is connected to the arm 30.
It is placed and fixed on the upper surface 30a of the.

Further, a ring-shaped yoke 53 made of a magnetic material is provided around the shaft 34 on the substrate 46, and a cylindrical inner yoke 54 is provided on the inner circumferential side of the bobbin 51 connected to this yoke 53. A pair of permanent magnets 55a, 55b are fixed to outer yokes 58a, 58b, respectively, and are installed facing each other, and the focusing coil 32 is placed between the pair of permanent magnets 55a, 55b and the inner yoke 54, respectively. A magnetic flux is generated that crosses the tracking coil 33, and the bobbin 51 is displaced along the shaft 34 depending on the magnitude and direction of the magnetic flux, the current flowing through the focusing coil 32 and the tracking coil 33, and focusing is performed. The drive is also rotated around the shaft 34 to perform tracking drive. Furthermore, the other parts except the objective lens 27 are covered with a case 56. Note that FIG. 4B is a partially sectional plan view with the case 56 removed.

For example, as shown in FIGS. 6A and 6B, when viewed in the vertical direction of the compact disk 60,
When the height of the optical head 61 is H, the width is W, and the length is L, in the conventional configuration shown in FIG.
It was about W27mm x L72mm, but the same specifications,
If the optical head 61 with high performance has the configuration of this embodiment shown in FIGS.
The length is about 77 mm, which allows it to be made significantly thinner, especially in the height direction, making it possible to create a player that is suitable for thin and small compact discs.

Note that the present invention is not limited only to the embodiments described above, and numerous modifications and changes are possible. For example, in the above embodiment, the focusing drive by the objective lens actuator is of the sliding type, and the tracking drive is of the rotation type, but the arm 30 protrudes from the objective lens actuator and the objective lens 27 is held at the tip thereof. As long as the structure is such that the objective lens is supported by a plate spring or the like, the objective lens may be supported by a plate spring or the like. Further, the polarizing prism 23 may be changed to a semi-transparent prism and the λ/4 plate 26 may be omitted. Furthermore, a mirror may be used instead of the reflecting prism 25.

The optical head of the present invention has a through hole for passing a light beam, has a wall thickness smaller than the wall thickness of the block in the first direction, and has a plate shape integrally formed with the block. A protrusion is disposed in the extending direction of the upper surface, and a lens peripheral portion surrounding the lens is placed and fixed on the upper surface of the plate-shaped protrusion around the through hole, and the plate-shaped protrusion in the information track direction is placed and fixed. The length dimension of the protrusion is set to be equal to or close to the external dimension of the peripheral portion of the lens, and the first and second Since the magnetic field generating means is arranged with a gap between the two coils, both the tracking drive and the focusing drive can be performed with high precision, and the assembly of the device is significantly simplified, and the degree of freedom in design is increased. , which has the advantage of being suitable for manufacturing automation.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the configuration of a conventional optical head;
2A to 2C are diagrams for explaining focus errors by the critical angle method, FIG. 3 is a perspective view showing the configuration of an example of the main part of the optical head of the present invention, and FIGS. 4A and B are FIG. 3 is a cross-sectional view and a plan view showing a specific configuration example of the optical head, FIGS. 5A and B are partial detailed views thereof, and FIGS. 6A and B are front views for explaining the effects of the present invention. and a bottom view. 21... Semiconductor laser, 22... Collimator lens, 23... Polarizing prism, 24... Polarizing film,
25...Reflection prism, 26...λ/4 plate, 27
...Objective lens, 28...Critical angle prism, 28
a... Optical surface, 29... Photodetector, 29a-29
d... Light receiving area, 30... Arm, 30a... Upper surface, 31... Objective lens actuator, 32...
... Focusing coil, 33 ... Tracking coil, 34 ... Shaft, 41 ... Inner frame, 42
...Outer frame, 43...Spring, 44...Screw, 45...
...Aperture, 46... Board, 47... Screw, 48...
Rotating member, 49... Holding member, 50... Screw, 5
1... Bobbin, 52... Elastic member, 53... Yoke, 54... Inner yoke, 55a, 55b... Permanent magnet, 56... Case, 57... Shaft fixing collar, 58a, 58b... Outer yoke, 60...
Compact disk, 61... Optical head, 70...
...Lens periphery, 70a...bottom surface.

Claims (1)

[Scope of Claims] 1. When a recording medium on which information is recorded in a track shape is irradiated with a light beam from a light source as convergent light through a lens, and the information is read by the reflected light, a light beam facing the medium surface of the recording medium is read. a first coil for driving the lens in a first direction perpendicular to the medium surface without tilting the lens optical axis; a second coil for driving the lens in a second direction parallel to the media plane and transverse to the information track; and a second coil for driving the lens in a second direction parallel to the media plane and transverse to the information track. and move together with the block, and the lens is driven in the first direction and the second direction by the action of magnetic flux generated from a magnetic field generating means fixed to the base. The optical head includes a plate-like protrusion that has a through hole for passing a light beam, has a wall thickness smaller than a wall thickness of the block in the first direction, and is integrally formed with the block. A peripheral portion of the lens disposed in the extending direction of the upper surface and further surrounding the lens is placed and fixed on the upper surface of the plate-shaped protrusion around the through hole, and a peripheral portion of the lens is placed and fixed on the upper surface of the plate-shaped protrusion in the information track direction. setting the length dimension to be equal to or close to the outer dimension of the peripheral portion of the lens;
An optical head characterized in that the magnetic field generating means is disposed at a position other than the space facing the plate-like protrusion in the first direction, with a gap between the first and second coils.