JPH0656664B2 - Light head - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tilt servo technique applied when correcting an inclination of an emission laser beam optical axis of an optical head used in an optical disc player with respect to a disc.

2. Description of the Related Art With an optical head whose numerical aperture of the objective lens is NA = 0.5 or more,
When a disc having a disc diameter of φ = 200 m / m or more is used as a medium, the disc warps or bends when the disc rotates, and an angle error occurs in the optical axis of the emitted laser light with respect to the disc. This angular error spreads the beam diameter in the tilt direction of the disk and adversely affects adjacent tracks.

Therefore, in this type of optical head, a tilt servo mechanism is incorporated in order to control the optical axis of the laser beam to follow the tilt of the disk and correct the tilt correctly. This tilt servo mechanism always detects the tilt of the disc at the laser light irradiation position by the tilt sensor provided in the optical head, feedback controls the tilt adjustment of the optical head based on the detection signal, and makes the laser light optical axis incident on the disc. This is for mechanically correcting an angle deviation and an error, whereby a tilt servo is performed to control the laser light optical axis to follow the tilt of the disk correctly.

Conventionally, this tilt servo mechanism has an LED (light emitting diode) with a lens that serves as a light source that illuminates the disk surface.
And a pair of optical sensors arranged on both sides of the LED, the reflected light of the light emitted from the LED to the disc is received by the pair of optical sensors, and the tilt servo signal is generated by the difference in the received light amount. Is what you get,
The foil was arranged in a system different from the optical system of the optical head.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the conventional tilt servo mechanism as described above, since the tilt servo system including the tilt sensor is configured separately from the optical system of the optical head, the laser of the optical system is A light source is required in addition to light, which is expensive, and the overall space is large, which is disadvantageous in terms of space saving.

Further, since the diffused light of the LED is used as the light source, there is a problem that the directivity is poor and accurate inclination detection cannot be performed at the edge portion of the disk. Further, the LED used as a light source has a large variation in the inclination of diffused light, which requires fine adjustment when it is attached to the optical head, and the attachment adjustment is troublesome, and at the same time, there is a drawback of lacking reliability.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a tilt servo mechanism for an optical head that has a simple structure, requires no space, has high sensitivity, and can perform tilt detection with high reliability, and at a low cost. It is what

Means for Solving the Problems According to the present invention, an area for allowing the collimated light formed by the collimator lens to go straight through / pass through is provided on the outer peripheral portion of the objective lens, and the collimated light emitted through this area is reflected by the disk. A pair of optical sensors that receive the diffracted light is arranged at a position facing the disk, and the optical axis of the emitted laser light is tilt-corrected with respect to the disk based on the differential output of the pair of optical sensors. A characteristic optical head.

The collimated light beam-formed through the working collimator lens goes straight through and passes through the region formed on the outer peripheral portion of the objective lens, and is emitted from the light source. The collimated light is reflected by the disk and returned as diffracted light, and the ± first-order light of the collimated light is detected by the pair of optical sensors. A servo signal for tilt servoing the optical head is obtained by the differential output. Therefore, a separate light source such as a conventional LED is not required, and the tilt servo system can be configured with the same system as the optical system of the optical head.

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

FIG. 1 is a schematic side view showing an optical system of an optical head according to the present invention, FIGS. 2 and 3 are perspective views showing main parts of a tilt sensor according to the present invention, and FIG. 4 shows a tilt mechanism of the optical head. It is a perspective view showing an example of an optical head drive mechanism including.

The objective lens 11 is supported by one end of the optical head body 10 facing the disk D so as to be driven in two axial directions orthogonal to the focus / tracking direction by a biaxial actuator (not shown). A semiconductor laser 12 is arranged at the other end of the optical head body 10. Semiconductor laser 1
In the optical axis direction in which the laser light F0 emitted from 2 reaches the objective lens 11, the diffraction grating 13 and the polarization beam splitter 1
4, a collimator lens 15, and a quarter-wave plate 16 are arranged in this order. Then, the return light F from the disc D
An astigmatism generating optical system element 17 and a photodetector 18 for receiving the converged light are arranged in the direction in which 1 is polarized through the polarization beam splitter 14, and focus error signal / tracking error signal and reproduction are performed. A signal detection system for signals is provided.

An upper portion of the optical head body 10 in which a biaxial actuator that supports the objective lens 11 is arranged is covered with an upper cover 19 having an opening corresponding to the objective lens 11. On the upper surface of the upper cover 19 facing the disk D, a pair of optical sensors 20 and 21 for tilt servo signal detection are arranged on both sides of the disk D with the objective lens 11 in the radial direction.

The objective lens 11 is, as shown in FIGS. 1 and 3,
A cylindrical portion 11a, a mounting flange portion 11b protrudingly formed on the outer periphery of the cylindrical portion 11a, a converging lens portion 11c formed in the inner center of the cylindrical portion 11a, and a transparent body such as glass or plastic integrally formed. Is. Cylindrical part 11a
Light-shielding films 22 and 22 are attached to the annular portion of the one end surface at symmetrical positions with the center line of the objective lens 11 corresponding to the radial direction of the disc D interposed therebetween. In this way, in the remaining portion of the cylindrical portion 11a of the objective lens 11 covered with the light shielding films 22 and 22, the transmission portion 111 of the laser light F,
112 is formed symmetrically with respect to the center in the radial direction of the disk D.

The entrance pupil diameter 1 of the lens portion 11c of the objective lens 11, that is, the inner diameter of the cylindrical portion 11a is smaller than the effective pupil diameter L of the collimator lens 15. Then, the objective lens 11
The outer diameter l'of the cylindrical portion 11a is equal to or slightly smaller than the effective pupil diameter L of the collimator lens 15.

As the objective lens and the collimator lens 15, for example, in an MO (photomagnetic) optical head, a focal length f = 5.
5 m / m, numerical aperture NA = 0.55, effective pupil diameter 6.05 m
/ M collimator lens, f = 3.9 m / m, NA =
An objective lens of 0.55 and an entrance pupil diameter of 4.3 m / m is used.

The laser beam F0 emitted from the semiconductor laser 12 passes through the diffraction grating 13 and the polarization beam splitter 14, and through the collimator lens 15, the effective pupil diameter L of the collimator lens.
It is shaped into a collimated light F0 'which is a circular parallel beam having the same diameter as. The collimated light F0 ′ reaches the objective lens 11 through the quarter-wave plate 16.

The collimated light F0 ′ is transmitted through the lens unit 11 of the objective lens 11.
A central portion having the same diameter as the entrance pupil diameter 1 corresponding to c is converged by this lens portion 11c, and the beam spot is irradiated on the surface of the disc D. Return light F1 reflected from the disc
Is a lens portion 11c of the objective lens 11, a quarter-wave plate 1
6, passed through the collimator lens 15, polarized through the polarization beam splitter 14, and guided to the photodetector 18 through the optical system element 17 for generating astigmatism.

On the other hand, the outer peripheral edge portion of the collimated light F 0 ′ from the center to the outside is the transmission portions 111, 1 of the cylindrical portion 11 a of the objective lens 11.
It goes straight through 12 without being affected by the lens action, and is irradiated onto the disk D surface. The emitted lights F2 and F3 are diffracted by the track groove of the disk D due to the reflection on the surface of the disk D. This diffracted light is the objective lens 11
Optical sensors 2 for tilt servo signal detection provided on both sides of the
Light is received at 0 and 21, respectively. The optical sensors 20 and 21 are arranged so as to receive only the + 1st and −1st order lights of the emitted lights F2 and F3, respectively. The tilt servo signal is detected by the differential output of the optical sensors 20 and 21. The tilt servo signal controls the tilt of the optical head, more specifically, the optical axis of the emitted laser light, following the tilt of the disk D. That is, the tilt mechanism of the optical head, which will be described later, is drive-controlled based on the tilt servo signals extracted from the optical sensors 20 and 21, and the optical head follows the inclination of the disk D and the inclination (angle) is corrected correctly.

The tilt sensor of the present embodiment uses the laser light F0 emitted from the semiconductor laser 12 through the collimator lens 15 as the light source and the outer peripheral light outside the center of the collimated light F0 '. The optical sensors 20 and 21 are arranged on both sides of the lens 11.

Next, the tilt mechanism for controlling the tilt of the optical head by the tilt output from the tilt sensor will be described.

A pair of guide shafts 31, 31 are arranged in parallel on a chassis base 30 that constitutes the player body. A frame-shaped head chassis 32 is mounted on the guide shafts 31, 31 so as to be slidable in the disk radial direction.
A linear drive coil 33 is attached to one end of the head chassis 32. A magnetic circuit 34 is arranged on the chassis base 30 corresponding to the coil 33. The coil 33 is combined with the yoke of the magnetic circuit 34 by fitting. On the other hand, a speed sensor 35 including a coil 351 and a magnetic circuit 30 is attached to the other end of the head chassis 32.

Supports 321 and 322 are erected on both sides of the head main body on the head chassis 32. Support 321,
The optical head body 10 is supported on the shaft 322 by shafts 36, 36 so as to be swingable. A line connecting the central axes T of the shafts 36, 36 serves as a tilt fulcrum for rotating the optical head body 10 in the tilt direction. The optical head main body 10 is rotated in the tilt direction about the tilt fulcrum T, and tilt correction is performed so that the laser light emitted from the optical head becomes perpendicular to the disk surface with respect to the warp and deflection of the disk D. . The tilt fulcrum T is set at a position where optimum tilt control can be performed according to the warp amount and warp angle of the disc D. A lever 37 extending in the direction opposite to the disk center O is attached to the lower end of one side of the optical head body 10. Lever 37
A pair of upper and lower shafts laterally protrude at the end of the, and guide rollers 38 and 39 are vertically mounted on the pair of laterally projecting shafts. One of the guide rollers 38, 39 is vertically movable, and is constantly urged toward the other guide roller 38 by a spring (not shown).

On the other hand, on both sides of the chassis base 30 corresponding to one side of the optical head 10, a pair of levers 40, 40 are rotatably supported by shafts near both ends in the moving direction of the optical head. There is. Between the levers 40, 40, a shaft 41 is stretched in parallel with the guide shaft 31. The shaft 41 is supported so as to be movable up and down with the pivot center of the levers 40, 40 as a fulcrum. One lever 4
0 (lever 40 on the front side in FIG. 4) is attached with a screw block 42 having a female screw on one side.
A feed screw shaft 43 rotatably supported on the chassis base 30 is screwed into the screw block 42. The worm wheel 4 is coaxially attached to the lower end of the feed screw shaft 43.
4 is attached. A drive motor 45 is arranged on the chassis base 30 on one side of the worm wheel 44. A worm gear 46 attached to the drive shaft of the drive motor 45 is meshed with the worm wheel 44.

The shaft 41 is sandwiched between a pair of guide rollers 38 and 39 provided on one side of the optical head 10.

The optical head 10 is driven by the rotation driving force of the drive motor 45.
By vertically moving the shaft 41 through the worm gear 46, the worm wheel 44, and the screw feeding mechanism, the shaft 41 is vertically swung about the tilt fulcrum.

The drive motor 45 is drive-controlled by a tilt servo signal extracted from the pair of optical sensors 20 and 21 that form the tilt sensor. Thereby, the optical head 10
The tilt is controlled according to the tilt of the disk along with the movement in the disk radial direction so that the optical axis of the emitted laser light is always perpendicular to the disk surface. That is, the inclination (angle) of the laser light is mechanically and automatically corrected.

According to the structure of the above-described embodiment, the component of the collimated light beam-shaped by the collimator lens that goes straight through the objective lens is used as the light source for the tilt sensor, so that a separate light source such as an LED is not required. Also, a tilt servo system can be configured in the same system as the optical system. Therefore,
It can be constructed at low cost, and it does not require a space and can save space.

In addition, since the collimated light of the optical head that goes straight out from the objective lens is used as a light source, it is possible to detect a tilt servo signal that has extremely high directivity, high sensitivity, and high reliability. And, unlike the conventional LED using as a light source, the adjustment work becomes unnecessary.

Further, unlike a conventional LED that uses diffused light, collimated light that goes straight along the outer peripheral edge of the objective lens 11 and is emitted is parallel light that is very close to the objective lens 11 and has extremely high directivity. Since the height is high, the tilt servo signal can always be detected accurately even when the optical head moves in the disk radial direction. In particular, accurate tilt servo signals can always be accurately detected in the vicinity of the edge portion where the warp or deflection of the disk, that is, the inclination becomes large.

As described in the above embodiment, a part of the collimated light passing through the outer peripheral edge of the objective lens 11 is partially shielded by the light shielding film 2.
If the light is blocked by 2, 22, it is advantageous in determining the orientation when adjusting the objective lens against the occurrence of coma aberration due to variations in individual dimensions during molding of the objective lens. The light shielding films 22 and 22 are not necessarily required. The intended purpose of the present invention can be sufficiently achieved without the light-shielding films 22 and 22.

The objective lens 11 is not limited to the one having the structure shown in the above embodiment.

As described above, according to the present invention, since the collimated light beam-formed by the collimator lens is used as the light source of the tilt sensor, it is not necessary to separately provide a light source such as an LED as in the conventional case. Further, the tilt servo system can be configured in the same system as the optical system of the optical head.
Therefore, the structure is simple and the cost can be reduced accordingly, and at the same time, no space is required and the space can be saved. Moreover, it is not necessary to attach the light source as in the conventional case, and the adjustment at the time of attachment is not required.

Further, according to the present invention, the collimated light that goes straight and goes out of the outer peripheral edge portion of the objective lens is irradiated in parallel to the disk, and the reflected light is received and detected by the optical sensor at a position close to the objective lens. Therefore, it is possible to detect the tilt servo signal with high sensitivity and high reliability.

[Brief description of drawings]

FIG. 1 is a schematic side view showing an example of an optical system of an optical head equipped with a tilt sensor according to the present invention, FIG. 2 is a perspective view of a main part of the optical head showing the tilt sensor according to the present invention, and FIG. FIG. 4 is a perspective view showing an objective lens of the optical head, and FIG. 4 is a perspective view showing an example of a tilt mechanism of the optical head driven by a tilt servo signal detected by a tilt sensor according to the present invention. 10 ... Optical head body, 11 ... Objective lens, 12 ... Semiconductor laser, 15 ... Collimator lens, 20, 21 ... Optical sensor for tilt error signal detection, 22 ... Shading film, F0 '... Collimated light , F2, F3 ... Emitted light for tilt sensor, D ... Disc,

Claims (1)

[Claims] 1. An optical head for shaping laser light emitted from a semiconductor laser into collimated light through a collimator lens and irradiating the collimated light onto a disk through an objective lens. Is provided at a position facing the disc, and a pair of optical sensors for receiving the diffracted light reflected by the disc of the collimated light emitted through this region is disposed at a position facing the disc. An optical head, wherein tilt correction (tilt servo) of the optical axis of the laser light with respect to the disk is performed based on dynamic output.