JPH0343694B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an apparatus for reading information by projecting a reading light spot onto an information track recorded spirally or concentrically on a recording medium such as a disk. Defocus correction for projecting spots, i.e. focusing;
and a device for correcting the relative positional deviation between an information track and a light spot projected by an objective lens, that is, tracking, and in particular an objective lens drive device that drives the objective lens in the optical axis direction and in a direction perpendicular to the information track. It is related to.

The above-mentioned reading device is known from the prior art, and in particular, a mechanism for driving the objective lens two-dimensionally in order to correct focusing and tracking with good responsiveness is disclosed in Japanese Patent Laid-Open No. 117337/1983. 1st
The figure shows this principle, and 1001 is the focusing direction 1002 is the tracking direction. 1 is an objective lens that moves in a focusing direction 1001 and a tracking direction 1002;
2 is a movable magnet fixed to the objective lens 1;
4 indicates the tracking direction 100 of the movable magnet 2
2, 301 and 302 are tracking direction drive coils symmetrically wound around the yoke 4, and 501 and 502 are parallel to the outer cylinder 12. spiral parallel diaphragms fixed to the diaphragms 501 and 502;
601 and 602 are parallel springs that connect the movable magnet 2 and the movable member 7; 8 is a cylindrical coil fixed to the movable member 7 for driving in the focusing direction; 9 and 10;
11 is a yoke of a magnetic circuit for driving in the focusing direction fixed to the outer cylinder 12, and 11 is a magnet of the magnetic circuit. That is, the movable member 7 is restricted to move only in the focusing direction 1002 by the diaphragms 501 and 502,
Objective lens 1 and magnet 2 are parallel springs 60
1 and 602, the movable member 7 is restricted to move parallel to the tracking direction 1002. However, the above structure has four main drawbacks as shown below. The first drawback is that, as mentioned above, the tracking direction 1 of this method is
002 is driven by a so-called movable magnet system. In other words, the lines of magnetic force 40 formed by the movable magnet 2 and the yoke 4
1 and 402 is unbalanced by the current flowing through the coils 301 and 302, and a force in the tracking direction 1002 proportional to the current acts on the magnet 2, thereby driving the lens 1. but,
This method has a fundamental drawback in that unbalanced force easily acts on the magnet 2 due to the influence of an external magnetic field, resulting in tracking errors and being susceptible to so-called magnetic disturbances. The second drawback is that the movable member 7 is moved in the focusing direction 1001.
Due to the diaphragms 501 and 502 used to restrict the movement to only a single movement, the range of movement in the focusing direction 1001 is restricted. For this reason, the permissible value of distortion in the focusing direction 1001 of the recording medium, so-called surface runout, is significantly restricted. Therefore, if the amount of surface runout is large, the movable range in the focusing direction must be increased by increasing the diameter of the diaphragm. A third drawback is the effect of restoring forces created by diaphragms 501 and 502. That is, the support member 7 and the diaphragms 501 and 502 are at a dynamic equilibrium point when no current flows through the coil 8, and the support member 7
A restoring force proportional to the deviation from this equilibrium point acts on . Therefore, when a so-called servo system is configured in which the amount of focusing error is detected by optical or electrical means and a current proportional to this amount is passed through the coil 8, the focusing residual deviation is proportional to the restoring force. This makes accurate focusing difficult. The fourth drawback is the diaphragm 501
Regarding the shape of 502, if a spiral diaphragm as shown in FIG. A rotational movement in the direction 1003 occurs, and accordingly, the lens 1 also causes a rotational movement about the optical axis, degrading the optical characteristics.
Furthermore, torsional mode vibration is induced in the parallel springs 601 and 602, further increasing the deterioration of the optical characteristics.

It is an object of the present invention to provide a small and compact device capable of correcting the defocus of a light spot projected onto a recording medium and correcting the relative positional shift between an information track and a light spot with high responsiveness by driving an objective lens two-dimensionally. The object of the present invention is to provide a lightweight objective lens driving device.

The present invention provides the objective lens with a coil that generates thrust in the tracking direction and the optical axis direction, and slides and supports a movable member that is movable in parallel only in the tracking direction so as to be movable only in the optical axis direction. This prevents the optical axis of the objective lens from wobbling and prevents mutual interference between movements in both directions.

In one embodiment of the present invention, the sliding portion is provided on a magnetic member of a magnetic circuit that drives the coil, thereby reducing the size of the device.

In one embodiment of the present invention, two sides of a rectangular coil parallel to the optical axis direction are used as a tracking direction driving coil, thereby reducing the size of the device.

In one embodiment of the present invention, a plurality of coils are arranged in the movable part to balance the weight of the movable part.

In one embodiment of the present invention, the center of thrust of the focusing coil substantially coincides with the center of gravity of the movable part, thereby preventing generation of rotational moment.

In one embodiment of the present invention, a similar effect can be obtained regarding a tracking coil.

In one embodiment of the present invention, the center of thrust of the tracking coil coincides with the center of gravity of the movable part in the same direction to obtain a similar effect.

In one embodiment of the present invention, the center of thrust of the tracking coil substantially coincides with the center of gravity of the sliding movable part to obtain a similar effect.

In one embodiment of the invention, the gap in the magnetic circuit is filled with magnetic fluid to obtain a damping effect.

In one embodiment of the present invention, the movable part is connected to the fixed part by a flexible member with large damping, thereby obtaining a damping effect.

An embodiment of the present invention will be described below with reference to FIGS. 2, 3, 4, and 5. Fig. 2 is a plan sectional view, Fig. 3 is a front sectional view taken along the line A-A' in Fig. 2, and Fig. 4 is a side sectional view taken along the line B-B' in Fig. 2.
FIG. 5 is an explanatory diagram of the external appearance. 1 is the objective lens, 2
4-1 and 24-2 are parallel springs that connect the objective lens and the slider 32; 32 is a guide yoke 2;
8 and a slider movable in the focusing direction 1001 with a slight gap; 25 is a coil 23-1 and 23-2 fixed to the objective lens 1 for driving in the tracking direction and driving in the focusing direction; A thin box-shaped bobbin 28 to which a coil 26 is fixed has a cylindrical surface that slides on the slider 32, and has a cylindrical surface that slides on the slider 32.
7-2 and magnets 29-1 and 29-2 constitute a magnetic circuit, and the coils 23 and 26 fixed to the bobbin 25 are connected to the coils 23 and 26 in parallel and linear gaps by the yokes 27-1 and 27-2. This is a guide yoke to be placed.

Regarding the magnetic circuit, as mentioned above, the guide yoke 2
8, consists of yokes 27-1 and 27-2 and magnets 29-1 and 29-2, and a gap is formed by the guide yoke 28 and yokes 27-1 and 27-2, and the magnetic flux in the gap is It is perpendicular to the cutting direction 1001 and the tracking direction 1002. Coils 23-1 and 23-2 and a coil 26 shown in FIG. 4 are fixed to the bobbin 25 disposed in the hollow. That is, the tracking direction driving coil 23-
1 and 23-2 have a thickness of about 1 to 4 layers, the innermost periphery has a substantially rectangular shape, and a predetermined number of wires are wound in a flat shape, which is then bent into a U-shape and parallel to the tracking direction. The sides are arranged symmetrically with respect to the optical axis, and the dimension 1010 of the same portion in the focusing direction is the same as that of the yokes 27-1 and 27-.
The yokes 27-1 and 27-2 are arranged symmetrically along the same direction with respect to the yokes 27-1 and 27-2. On the other hand, the coil 26 for driving in the focusing direction has a cylindrical shape concentric with the optical axis, and is connected to the guide yoke 28 and the yoke 27-1.
and 27-2. That is, the tracking direction drive coils 23-1 and 23-2 are not affected by the movement of the bobbin 25 in the focusing direction 1001, and are driven in the tracking direction 1002.
Generates thrust against. Similarly, the focusing direction driving coil 26 is connected to the bobbin 25.
A thrust force is generated in the focusing direction 1001 without being affected by the movement of the tracking direction 1002.

Regarding the mechanical relationship, the mechanical point of action of the thrust in the tracking direction 1002 generated by the tracking direction drive coils 23-1 and 23-2 is as follows:
Coils 23-1, 23-2 and 26, bobbin 2
5. Center of gravity of the equivalent movable part in the tracking direction of the objective lens 1 and the parallel springs 24-1 and 24-2 (hereinafter referred to as the tracking direction movable part), and the remaining parts of the parallel springs 24-1 and 24-2. and the center of gravity of the slider 32 and the center of gravity of the entire movable part. Also,
The mechanical point of action of the thrust of the coil 1001 for driving in the focusing direction is arranged so as to substantially coincide with the center of gravity of the entire movable part.

Regarding the focusing direction 1001 operation, the bobbin 25 is connected to the slider 32 via the objective lens 1 and the parallel springs 24-1, 24-2, and the parallel spring 24
-1 and 24-2 are tracking directions 1002
has low rigidity, and the focusing direction 1001
Since the bobbin 25 has high rigidity, the bobbin 25 moves parallel to the slider 32 only in the tracking direction. Here, the slider 32 slides on the guide yoke 28 with a small gap, and is allowed to move only in the focusing direction 1001.As mentioned above, the center of thrust of the coil 26 and the center of gravity of the movable part are Since they almost match, the moment acting around the center of gravity is also small. Therefore, the objective lens moves in the focusing direction 1001 in response to the thrust of the coil 26. At this time, the relative angular deviation (hereinafter referred to as optical axis deflection) of the optical axis of the objective lens with respect to the center axis of the guide yoke is very small.

Regarding the operation in the tracking direction 1002,
Due to the functions of the parallel springs 24-1, 24-2 and the slider 32, the objective lens 1 moves in translation in the tracking direction 1002 in response to the thrust of the coils 23-1 and 23-2. At this time, as described above, the thrust centers of the coils 23-1 and 23-2 almost coincide with the center of gravity of the movable part in the tracking direction, and the moment acting around the center of gravity is very small. The deflection of the optical axis due to directional movement is slight. Furthermore, interference between operations in the focusing direction and tracking direction is small, and errors in each direction can be corrected by currents flowing through the respective coils. Furthermore, since the magnetic circuit and the movable part are independent and can be assembled from one direction, the manufacturing process can be simplified.

Further, the guide yoke 28 and the yoke 27-
By filling the gap formed by 1 and 27-2 with magnetic fluid, the damping characteristics of the movable part in the focusing direction and the tracking direction can be improved.

Furthermore, as shown in FIG. 6, by connecting the bobbin 25 and the magnetic circuit with a stretchable high damping material (such as rubber) 33-1 to 33-4, the damping characteristics of the movable part in the focusing direction and the tracking direction can be improved. can be improved.

According to the present invention, an objective lens fixed to a coil that applies thrust in the focusing and tracking directions is connected to a slider that slides in the focusing direction via a parallel spring that bends in the tracking direction. It is possible to obtain a compact objective lens drive device with a large movable range, which has little interference in movement in mutual directions and has little optical axis deflection.

In addition, by filling the gap in the magnetic circuit with magnetic fluid, or by connecting the movable part to the magnetic circuit with an elastic damping material,
Good damping characteristics can be obtained.

[Brief explanation of drawings]

1a and 1b are a plan sectional view and a front sectional view showing an example of a conventional objective lens driving device, FIG. 1c is a plan view of a diaphragm, and FIGS. 2 to 5 show an embodiment of the present invention FIG. 2 is a plan sectional view thereof,
FIG. 3 is a sectional view taken along line A-A' in FIG. 2, FIG. 4 is a sectional view taken along line B-B' in FIG. FIG. 3 is a plan view showing an example.

Claims (1)

[Claims] 1 an objective lens, a first movable member having a cylindrical surface centered on the optical axis direction of the objective lens and movable only in the optical axis direction, connecting the objective lens and the first movable member; and an objective lens support means that is bent in a direction perpendicular to the optical axis and the information track (hereinafter referred to as the tracking direction) and supports the objective lens so as to be movable parallel to this direction, and a direction perpendicular to the tracking direction and the optical axis. a magnetic circuit having a gap having a magnetic flux; a first coil concentric with the optical axis direction and disposed in the gap;
An objective lens driving device comprising: a second coil disposed in the gap; and a second movable part connecting the objective lens and the first and second coils.