JPS62121933A - Diffraction grating adjustment device for optical pickup head - Google Patents

Abstract

PURPOSE:To improve work efficiency by controlling an actuator so as to carry out automatic adjustment with the aid of a tracking error signal when a diffraction grating is adjusted so that the prescribed off-set angle can be made with respect to a straight line connecting a main beam and a pair of subbeams. CONSTITUTION:Laser light is split into the main beam 28 and the subbeams 29a and 29b located at both sides of said main beam by the diffraction grating 12. By turning the diffraction grating 12, it turns out to be the diffraction grating device of an optical pickup head 11 adjusting the subbeams 29a and 29b. The actuator 15 which is engaged with the side of the diffraction grating 12 and turns the diffraction grating device in the outer periphery, and a control circuit 33 which inputs a signal corresponding to the difference between reflected light beams by the subbeams 29a and 29b and controls the actuator 15 so that the difference signal can be maximized, are provided. Accordingly products excellent in stable performance can be obtained and a yield can be improved.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a diffraction grating for an optical pickup head that adjusts the angle of the diffraction grating for dividing a laser beam into three parts: a main beam and sub beams located on both sides of the main beam. Relating to an adjustment device.

[Technical blueprint for invention]

Optical pickup heads used for audio, video, or information processing optical discs such as compact discs are
As is well known, the main beam is irradiated onto the track of a compact disk, and the information on the track is read by the reflected light.A tracking servo system is used to ensure that the main beam accurately traces the track.
It is necessary to do 1.

To this end, conventionally, in addition to the main beam, sub beams are generated on both sides of the main beam using a diffraction grating, and the straight line connecting the sub beams via the main beam is set to have a certain offset angle with respect to the track direction. ing. In this way, when the main beam is on-track, the amount of light reflected by each sub-beam is equal, but when the main beam is off-track, there will be a difference in the reflected light ω from each sub-beam, which will generate a tracking error signal. . The tracking servo system controls the position of the optical pickup head based on this tracking error signal so that it becomes zero, so that the main beam always accurately traces the 1-rack.

In order to perform the above-described control, it is necessary to set the offset angle to an optimal value in the manufacturing process of the optical pickup head. That is, it is necessary to adjust the offset angle so as to generate the largest tracking signal when the main beam goes off-track.

As mentioned above, the main beam and the pair of sub beams are created by dividing the laser beam into three parts using a diffraction grating.
The offset angle can be changed by rotating the diffraction grating.

[Problems with background technology]

Conventionally, for the above adjustment, an operator manually operates a bottle that engages around the outer periphery of the diffraction grating to rotate the diffraction grating.
For example, adjustments were made while visually checking the tracking error signal displayed on the oscilloscope screen.

However, the above-mentioned adjustment work requires manual labor from beginning to end, the resolution of the adjustment mechanism is small, and tracking error signals must be visually confirmed using an oscilloscope, etc., making it difficult to improve reliability and reducing yield. There was a problem with that.

(Object of the Invention) The object of the present invention is to provide a diffraction grating adjustment device for an optical pickup head that automatically adjusts the diffraction grating using a tracking error signal, thereby eliminating the need for human labor and obtaining a product with stable and good characteristics. It is about providing.

[Summary of the invention]

The present invention provides a diffractive optical pickup head that adjusts the position of the sub beams by rotating a diffraction grating that divides a laser beam into three into a main beam and sub beams located on both sides of the main beam in the direction of its outer circumference. In the grating adjustment device, an actuator that engages with the diffraction grating side and rotates it in the outer circumferential direction, and an actuator that inputs a signal corresponding to the difference in light reflected by each of the sub-beams and inputs a signal corresponding to the difference in reflected light from each of the sub-beams so that the difference signal is maximized. The main beam is off-track in advance, and in this state, the actuator rotates the diffraction grating until the difference signal, that is, the tracking error signal reaches a maximum. ,
This is to adjust the angle.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 1, reference numeral 11 denotes an optical pickup head, which has a diffraction grating 12. The diffraction grating 12 divides the laser beam into three parts, and divides the laser beam into three parts as a main beam and a pair of sub beams located on both sides of the main beam. Irradiate onto the 1-rack of an optical disk such as a disk. The diffraction grating 12 is held by a holder 13 having a circular outer diameter, and is supported by the pickup head 11 so as to be rotatable along the outer circumferential direction of the holder 13.

An actuator 15 is configured to rotate the diffraction grating 12. That is, reference numeral 16 denotes a rotating body, which has a shaft shape and is supported by a cylindrical holder 17 so as to be movable in both the axial direction and the outer circumferential direction. The lower end of the rotating body 16 projects downward from the lower end J of the holder 17 and is integrally connected to the disc 18. Further, an eccentric pin 19 is integrally provided at the upper end of the rotating body 16 and is eccentrically arranged with respect to the center of rotation. This eccentric pin 19 engages with a groove 13a formed on the outer circumference of the holder 13 of the diffraction grating 12, and rotates the diffraction grating 12 side in the direction of its outer circumference.

An A-me wheel 21 is attached to the outer periphery of the cylindrical holder 17.
a is integrally provided, and a disk 22 is integrally provided at the lower end. The worm wheel 21 a meshes with a worm gear F 21 b directly connected to a pulse motor 23 to form a worm gear mechanism 21 . Also,
The disc 22 has a guide rod 24 planted downward. This guide rod 24 is connected to the disc 1 on the side of the diffraction grating 12.
It engages with a notch 18a provided in 8. Further, a repulsion spring 25 is provided between the lower end 7 of the guide rod 24 and the lower surface of the disc 18.

The actuator 15 is configured to be able to move up and down, and during adjustment work is driven upward by a drive mechanism (not shown) to move the eccentric pin 19 into the groove 13a on the diffraction grating 12 side as shown in FIG. engage inside.

Figure 2 shows the control system. In the figure, 27 is a track of an optical disc such as a compact disc, 28 is a main beam,
29a and 29b are a pair of sub-beams, and each of these beams is created by dividing the laser beam into three by the diffraction grating 12. 30a and 30b are photoelectric converters;
It receives the reflected light from the beams 29a and 29b, and outputs an electrical signal corresponding to the amount of reflected light. These electrical signals are sent to a differential amplifier 32 via corresponding amplifiers 31a and 31b.
is input. The differential amplifier 32 compares the above two inputs,
The difference signal, ie, the tracking error signal, is output. 33 is a control circuit which inputs the difference signal and controls the pulse motor 23 shown in FIG. 1 until this difference signal reaches the maximum value.
Rotate.

In FIG. 2, a main beam 28 and a pair of sub beams 29a
, 29b has a certain offset angle with respect to the direction of the track 27. In this state, when the main beam 28 is on track, the sub beams 29a,
The reflected light from 29b becomes uniform, and no tracking error signal is output. Therefore, by controlling the position of the optical pickup head 110 so that the tracking error signal is always zero during use, the main beam 28 can always be kept on track.

Adjustment work to obtain such a predetermined offset angle is performed as follows. First, since it is before adjustment, the main beam 28
It is assumed that a straight line connecting the pair of sub-beams 29a and 29b is parallel to the track 27.

Further, when performing the adjustment, the center of the main beam 28 is set in advance to an off-track state where it is deviated from the center of the track 27. This off-track state can be easily overcome by turning off the tracking rib system. Even in this off-track state, the straight line connecting the main beam 28 and the sub beams 29a and 29b is 1-rack 27.
If parallel to the direction of
That is, almost no tracking error signal is generated.

Next, the actuator 15 shown in FIG. 1 is rotated upward, and its eccentric pin 19 is engaged in the groove 13a on the diffraction grating 12 side, as shown in FIG. 3(C). In this case, even if the upper end of the eccentric pin 19 and the bottom of the flange 13a come into contact, kl at that time is
Since it is absorbed by the spring 25 provided between the two, there is no problem.

In this state, the control circuit 33 rotates the pulse motor 23. The rotation of the pulse motor 23 is transmitted to the cylindrical boulder 17 via the worm gear mechanism 21, and from the disc 22 integrated therewith, the disc 18 and the rotating body 16 integrated therewith are rotated via the guide bar 24. This rotation of the rotating body 16 causes the eccentric pin 19 to rotate the diffraction grating 12 side along its outer circumferential direction, as shown in FIG. 3@(C).

As the diffraction grating 12 rotates, the offset angle with respect to the direction of the straight track 27 connecting the main beam 28 and the sub beams 29a and 29b changes continuously.

Here, as described above, since the main beam 28 is set in an off-track state where it deviates from the track 27, when the offset angle occurs, the pair of sub beams 29a.

There is a difference in the intensity of the reflected light by the differential amplifier 32.
A tracking error signal is generated. This i-racking error signal fluctuates as the off-seller 1-angle changes.

The Zl control circuit 33 inputs the tracking error signal, stops the pulse motor at the angle r at which the tracking error signal becomes maximum, and finishes the adjustment of the diffraction grating 12.

By the above adjustment, the offset angle is adjusted to the optimum angle at which the largest 1 to racking error signal occurs when the main beam 28 goes off-track.

〔Effect of the invention〕

As described above, according to the present invention, when adjusting a diffraction grating so that a straight line connecting a main beam and a pair of sub beams forms a predetermined offset angle with respect to the track direction, a tracking error signal is used. Since the actuator is controlled and automatic adjustment is performed, work efficiency is significantly improved compared to the conventional method where Akane manually adjusts the diffraction grating while visually observing the tracking error signal displayed on an oscilloscope. Therefore, it is possible to obtain products with stable performance and improved yield.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view showing an embodiment of the diffraction grating adjustment device for an optical pickup head according to the present invention, FIG. 2 is a control circuit diagram thereof, and FIG. 3 shows the adjustment state of the diffraction grating by the device shown in FIG. FIG. 11... Optical pickup head, 12... Diffraction grating, 1
3a...Groove, 15...Actuator, 16...Rotating body, 19...Eccentric pin, 2-tooth gear mechanism, 23...
・Pulse motor, 28... Main beam, 29a, 29
b...Sub beam, 33...Control circuit.

Claims (3)

[Claims] (1) A diffraction grating for an optical pickup head that divides the laser beam into three parts: a main beam and sub-beams located on both sides of the main beam, and rotates the diffraction grating in the outer circumferential direction to adjust the position of the sub-beams. The adjustment device includes an actuator that engages with the diffraction grating and rotates it in the outer circumferential direction, and a signal corresponding to the difference in light reflected by each of the sub-beams that is input to the actuator so that the difference signal is maximized. A diffraction grating adjustment device for an optical pickup head, comprising: a control circuit for controlling; (2) The actuator has an eccentric pin provided eccentrically with respect to the rotation center of the rotating body, and this eccentric pin is engaged with a groove provided on the outer periphery of the diffraction grating side, and the rotation of the rotating body causes diffraction to occur. A diffraction grating adjustment device for an optical pickup head according to claim 1, characterized in that the grating is rotated. (3) The diffraction grating adjustment device for an optical pickup head according to claim 2, wherein the actuator has a pulse motor and a worm gear mechanism that transmits the rotational force of the pulse motor to a rotating body.