JPH0474782B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a device for reading information by illuminating an information track recorded on a recording medium with a light spot, in order to correct the relative positional deviation between the information track and the light spot caused by an objective lens. This invention relates to a driving device that drives an objective lens two-dimensionally in a direction perpendicular to its optical axis and an information track.

The above-mentioned information reading device is used for video discs, etc., and focuses on correcting the positional deviation of the information track in the same direction as the irradiation beam, and corrects positional deviation in the direction perpendicular to the information track and the beam optical axis. is called tracking,
Various methods have been proposed in the past.

As one of the methods proposed, a tracking mirror that swings around a single axis is placed in the optical path between the light source and the objective lens and tracking is performed by swinging the light beam, but this method is not fully satisfactory. It is difficult to obtain exponent precision and response characteristics, and the objective lens has drawbacks such as astigmatism because the light rays are obliquely incident on the optical axis of the objective lens. In addition, in order to eliminate such defects, the objective lens or its holding frame is supported by an elastic support member made of a leaf spring or rubber, and the objective lens is adjusted perpendicular to its optical axis and information track based on focus and tracking error signals. A method of linearly sliding displacement in a direction has been proposed.
However, moving the optical system in parallel in a linear manner in a pick-up with extremely limited space requires a very complicated mechanism due to the relative positional relationship with the magnetic coil, and there is also the problem that the tracking width cannot be secured very much. There is. Furthermore, when a spring is used as the elastic support material, it tends to resonate easily, and when rubber is used, there are problems in terms of temperature characteristics and aging. Further, there are voice coil systems and piezoelectric systems as tracking mechanisms, but the voice coil system has drawbacks such as difficulty in reducing the size and weight, and the piezoelectric system cannot obtain the necessary force.

The present invention eliminates the above-mentioned drawbacks, does not require extra space for moving the optical system, allows tracking over a wide range with a relatively simple mechanism, and is compact enough to obtain the necessary power. The objective is to provide a lightweight two-dimensional objective lens driving device.

That is, the present invention provides an optical system that focuses and irradiates a light beam onto a record carrier on which readable or writable information is recorded by optical means, a lens barrel that supports this optical system, and a lens barrel that moves this lens barrel. In an optical pickup consisting of a driving means, the optical axis of the condensing optical system is mounted eccentrically with respect to the central axis of the lens barrel, and the optical system is moved by swinging and rotating the lens barrel about its central axis. The gist is that tracking is performed by moving the optical axis in a direction that traverses the information track on the record carrier.

According to the present invention, since the cylindrical lens barrel is rotated around its central axis, no extra space is required for the movement compared to the conventional case where the lens barrel is moved linearly in parallel. Further, such rotational movement can be achieved very quickly and smoothly with a relatively simple structure by using, for example, a ring-shaped electromagnet surrounding the lens barrel as described below.

The present invention will be described in detail below with reference to the drawings.

1A and 1B are a vertical sectional view and a plan view showing the lens portion of the optical pickup according to the present invention, in which numeral 1 represents a movable lens barrel and numeral 2 represents an objective lens. The objective lens 2 has its optical axis 4 parallel to the central axis 3 of the lens barrel in the traveling direction 1 of the information track 10 on the information recording carrier.
1 by a distance l ₀ and fixed to the lens barrel 1.

As an example, the objective lens 2 has a refractive index on the central axis 4.
It is a gradient index lens consisting of a transparent glass or plastic cylinder with parallel planes at both ends and a distribution that decreases parabolically in the radial direction from the top to the periphery.

A light beam is introduced into a lens barrel 1 from above in FIG. 1, focused by an objective lens 2, and irradiated onto a track 10 on an information recording carrier.

The lens barrel 1 swings and rotates around its central axis 3 by a mechanism to be described later, and in conjunction with this, the objective lens 2 moves in a direction in which its central axis 4 crosses the information track 10 of the information recording carrier. .

That is, an angle of 2 to both sides of the information track 10
By swinging and rotating the lens barrel 1 by θ
Error correction tracking can be performed over a width range of 2l ₀ cosθsinθ. The eccentric distance l ₀ is generally about 2 m/m to 8 m/m. FIG. 2 shows an embodiment of a mechanism for performing a tracking operation.

In FIG. 2, the central axis 3 of the movable lens barrel 1 is
An objective lens 2 having an optical axis 4 is mounted at a certain distance from the lens, and a magnetic body 7 is similarly fixed within the lens barrel 1 at right angles to the central axis 3. On the other hand, the external magnetic circuit has a ring structure surrounding the lens barrel 1 by bonding arc-shaped permanent magnets 5-1 and 5-2 with the same polarity to yokes 6-1 and 6-2. This yoke 6-1,
Tracking coils 8-1 and 8-2 are wound around 6-2.

Next, the tracking operation will be explained. Figure 2A shows the situation when no error correction current is applied to the tracking coils 8-1 and 8-2, and the magnetic fluxes emitted from the N poles of the permanent magnets 5-1 and 5-2 are as follows: It passes through the inside of the yoke 6-2, flows out from the balanced point D, and enters the magnetic body 7 inside the movable lens barrel 1.

Similarly, on the S pole side, magnetic flux penetrates into the yoke 6-1 from the balanced point C.

On the other hand, the tracking coils 8-1 and 8-2 have second
When a current is applied as shown in Figure B, the magnetic flux excited by the coils 8-1 and 8-2 causes the yokes 6-1 and 6-2 to
The balance point of the magnetic flux distribution within is moved from C and D along the circumference of the yokes 6-1 and 6-2 to points E and F, and the magnetic flux inside the movable lens barrel 1 is adjusted accordingly. The body generates a rotational moment about the central axis 3, and the optical axis of the objective lens 2 moves from 4 to 4A.

In this way, tracking coils 8-1, 8-2
By controlling the current flowing through the coil, a tracking operation proportional to the coil current can be performed.

Figure 3 shows an example of an optical pickup structure in which a focusing operation is added to a tracking operation.In addition to the lens barrel rotation mechanism shown in Figure 2, a folded flange is formed on the outer circumference of the end of the lens barrel 1, and The focusing coil 9 is wound around the coil 9.
Ring-shaped yokes 11 and 12 are placed on both sides of the yoke, and a magnetic circuit magnet 10 is arranged between these yokes and housed in an exterior case 13.

A stopper member 14 is provided on the outer wall of the lens barrel 1 above the yoke 12 to prevent the movable lens barrel 1 from falling off when no current is applied to the focusing coil 9.

When performing focusing, the coil 9 can be adjusted by changing the current of the focusing coil 9.
is moved in and out between the yokes 11 and 12 to move the lens barrel 1 to the third
This is done by moving it up and down in the figure.

According to the above structure, the movable lens barrel 1 is not supported by an elastic support and is in a free state, so it is not affected by adverse effects such as resonance caused by the elastic support, changes over time, and temperature dependence of the spring constant. can be avoided.

In addition, since the lens barrel is oscillated and rotated around its own center, the inertia force is smaller compared to a method in which the optical system is placed at the center of the lens barrel and the lens barrel revolves and oscillates, allowing for smoother movement and faster response times. A tracking operation with excellent fast followability can be achieved.

[Brief explanation of the drawing]

Figures 1A and 1B are longitudinal and cross-sectional views of a lens support barrel showing an embodiment of the present invention, and Figure 2 shows a mechanism for rotationally driving the lens support barrel shown in Figure 1 to perform tracking. FIG. 3 is a cross-sectional view showing an example, in which A is a state in which no driving current is applied to the coil; B is a state in which current is applied to the coil; and FIG. FIG. 1... Lens barrel, 2... Objective lens, 3... Lens barrel center axis, 4... Lens optical axis, 5-1, 5-2... Permanent magnet, 6-1, 6-2... Yoke, 7... Magnetic material, 8-1, 8-2... Coil, 10... Information track, 11... Information track moving direction.

Claims (1)

[Claims] 1 Consists of an optical system that focuses and irradiates a light beam onto a record carrier on which readable or writable information is recorded by optical means, a lens barrel that supports this optical system, and a driving means that moves this lens barrel. In the optical pickup, the condensing optical system is installed in the lens barrel with its central axis eccentric to the central axis of the lens barrel, and as the driving means, a magnetic material is placed inside the lens barrel at right angles to the central axis. At the same time, a ring-shaped external magnetic circuit is arranged outside the lens barrel, in which arc-shaped magnets with the same polarity are attached to a pair of yokes, and tracking coils are wound around these yokes, and the driving means drives the lens barrel. An optical pickup that performs tracking by swinging and rotating the optical system around its central axis to move the central axis of the optical system in a direction that traverses information tracks on a record carrier.