JPH0416860B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical reading device that detects a tracking error using a main beam and a sub beam.

When reading information tracks optically recorded on a disk-shaped recording medium (hereinafter referred to as disk), focus control is required to correct the focal position for disk warpage and surface wobbling, and radial direction correction for disk eccentricity. Tracking control is required to correct the deviation of the optical spot, and one of the latter tracking control methods is a method of performing control using a main beam and a sub beam.

In this method, as shown in Fig. 1, the main beam 1 and the sub beam 2 formed by a diffraction grating are arranged so that the direction in which they line up is at a certain angle θ with respect to the information track 3, and the main beam 1 is When the main beam 1 is on track 3, the amount of reflected light from the two sub-beams 2 is equal, and as shown in Figure 2, when the main beam 1 deviates from the track 3 due to eccentricity of the disk, the two sub-beams This produces a difference in the amount of reflected light between the two, and detects a tracking error. In this case, it is necessary to accurately adjust the angle θ, and as shown in Figure 3, θ=0°.
If the angle θ becomes too large as shown in FIG. 4 and the sub beam 2 deviates from the track 3, accurate tracking cannot be obtained.

This angle θ can be adjusted by rotating the diffraction grating within the grating plane, but even if the optical pick-up itself is adjusted correctly, it is difficult to adjust the angle θ by rotating the diffraction grating within the grating plane. When the trajectory of the light spot accompanying the radial movement of the pick-up holder does not pass through the center of rotation of the disk due to an installation error, an error occurs in the angle .theta.. That is, the fifth
In the figure, the trajectory of the light spot is at the center of rotation O and h
If an error occurs by a distance of , an angular error of α=sinh/r≈h/r occurs, where r is the distance between the spot position and the center of rotation. This error becomes larger as the optical spot moves toward the inner circumference, and when errors due to eccentricity of the disk are added, the conditions shown in FIGS. 3 and 4 described above occur, and accurate tracking is no longer possible. Therefore, when the optical pick-up is mounted on the pick-up holder, it is necessary to adjust the angle between the direction in which the main beam and sub beam are lined up and the information track.

In conventional optical reading devices using gas lasers, the overall size of the optical system is large, so this system is constructed with a leaf spring and screws that allow the angle of the diffraction grating to be adjusted while it is built into the optical reading device. I was able to install the angle adjustment mechanism.

However, as optical pickups have become smaller by using semiconductor lasers, and optical components such as diffraction gratings have also become smaller, the diffraction grating itself has to be adjusted using an external adjustment jig after being attached to the pick-up holder. It becomes difficult to rotate and adjust the angle. In addition, if only an optical pick-up is used as a single product, even if the angle of the diffraction grating is adjusted internally, the set maker will have to reinstall it on a pick-up holder equipped with a radial feed mechanism. Adjustment is required, and adjusting the internal diffraction grating again is very complicated and difficult.

Therefore, an object of the present invention is to adjust the angle between the optical pick-up and the main beam when the optical pick-up is mounted on a pick-up holder having a radial feeding mechanism. As long as the alignment direction with the sub beam and the angle with the information track can be optimally adjusted, and the diffraction grating in the optical pickup is coarsely adjusted, any assembly errors can be absorbed after it is assembled as a set. It is an object of the present invention to provide an optical reading device that can be freely adjusted.

An embodiment of this invention is shown in FIG. This figure is a plan view, and for the disk surface to be reproduced,
It is a view seen from the vertical direction. An optical pick-up 7 having a semiconductor laser 4, a focus lens 5 and a photodetector 6 is attached to an adjustment screw 9.
It is fixed to the pick-up holder 8 by means of a screw. The pick-up holding base 8 is a guide shaft 10a, 1
It is possible to move in the radial direction (horizontal direction in the figure) along 0b. One guide shaft 10b
is a feed screw, and the pick-up holder 8 can be moved by rotating this guide shaft 10b with a motor. The mounting adjustment screw 9 also serves as an angle adjustment mechanism for adjusting the angle θ between the direction in which the main beam and sub-beam are lined up and the direction of the information track.
By tightening the other, the optical pick-up 4 can be rotated about the axis perpendicular to the plane of the paper around the engagement part between the recess 11a and the protrusion 11b, which serves as a fulcrum mechanism, and the pitch of the mounting adjustment screw 9 can be shortened. By doing this, you can make as many fine adjustments as you like. In other words, two mounting adjustment screws 9
The overall angle of the optical pickup 4 can be changed depending on the degree of tightening, and as a result, the angle between the direction in which the main beam and sub beams are lined up and the information track can be changed.

Note that, as shown in FIG. 7, the fulcrum mechanism may be formed by fitting the hole 12 and the support shaft 13, and the fulcrum may be aligned with the central axis of the focus lens. Also, the 8th
As shown in the figure, by using a spring member 14 on one side of the protrusion 11a that serves as a fulcrum, it is also possible to adjust with a single mounting adjustment screw 9. In this case, the spring member 14 and the mounting adjustment screw 9 constitute an angle adjustment mechanism.

The device includes a fulcrum mechanism that supports an optical pick-up on a pick-up holder so as to be rotatable in a plane parallel to the disc-shaped recording medium, and a fulcrum mechanism that is provided on the pick-up holder and rotates the optical pick-up around the rotational fulcrum of the fulcrum mechanism. With the simple structure of providing an angle adjustment mechanism for moving the optical pick-up, when the optical pick-up is attached to the pick-up holder, the angle adjustment mechanism can be used to adjust the angle between the optical pick-up and the pick-up holder. It is possible to optimally adjust the alignment direction of the main beam and sub-beam and the angle between the information track, and there is an effect that adjustment to absorb assembly errors can be easily performed.

[Brief explanation of drawings]

Figures 1 to 4 are positional relationship diagrams of the main beam, sub-beam and information track in various states;
Fig. 5 is an explanatory diagram when generating an angular error, Fig. 6 is a plan view of one embodiment of the present invention, Fig. 7 is a perspective view of another embodiment, and Fig. 8 is a diagram of still another embodiment. FIG. 1...Main beam, 2...Subbeam, 3...Truck,
4... Semiconductor laser, 5... Focus lens, 6...
Photodetector, 8...Pickup holding stand, 9
...Mounting adjustment screw, 10a, 10b...Guide shaft, 11a...Recess, 11b...Protrusion, 12...Hole, 1
3... Support shaft, 14... Spring member.

Claims (1)

[Scope of Claims] 1. A pick-up holder that moves along the radial direction of a disc-shaped recording medium, and a main beam and a sub-beam irradiated onto the disc-shaped recording medium to form a concentric or spiral shape on the disc-shaped recording medium. an optical pick-up that detects a tracking error of a track optically recorded on the disk; a fulcrum mechanism that allows the optical pick-up to be rotatably supported on the pick-up holder in a plane parallel to the disc-shaped recording medium; An optical reading device comprising: an angle adjustment mechanism provided on the pick-up holding base to rotate the optical pick-up around a rotational fulcrum of the fulcrum mechanism. 2. The fulcrum mechanism according to claim 1, wherein the fulcrum mechanism comprises a recess provided on one of the side surface of the optical pickup and the pick-up holder, and a protrusion provided on the other side and engaged with the recess. Optical reader. 3. The fulcrum mechanism is provided with a support shaft that is provided on one of the back face of the optical pickup with respect to the reading side and the pick-up holding base and faces perpendicular to the disk-shaped recording medium, and a support shaft that is provided on the other side and rotates on the support shaft. 2. The optical reading device according to claim 1, further comprising a hole that can be fitted into the optical reading device. 4. Claim 1, wherein the angle adjustment mechanism comprises a plurality of adjustment screws that are arranged on both sides of the rotation fulcrum of the fulcrum mechanism and connect the pick-up holder and the optical pick-up. Second
The optical reading device according to item 1 or 3. 5. The angle adjustment mechanism includes an adjustment screw disposed on one side of the fulcrum mechanism with respect to the rotation fulcrum to connect the pick-up holding base and the optical pickup, and an adjustment screw disposed on the other side with respect to the rotation fulcrum of the fulcrum mechanism to connect the pick-up holding base and the optical pickup. The optical reading device according to claim 1, 2 or 3, comprising a spring member that connects a pick-up holder and said optical pick-up.