JPH04102235A - Objective lens driving device - Google Patents

Abstract

PURPOSE:To obtain satisfactory servo characteristic by eliminating a force to rotate a movable part by deviating the driving point of a driving means from the optical axis of an objective lens, and comprising the magnetic gap of a pair of magnets of S-pole and N-pole. CONSTITUTION:The objective lens 21 is fixed on a lens holder 22, and a focusing coil 23 and a tracking coil 24 on the hollow part of the lens holder 22, which comprise the movable part. Two magnets 28 are fixed on a yoke 27 confronting and keeping a gap between unlike poles of S-pole and N-pole, respectively, which form a single magnetic gap. A current flows in a direction of Z-axis on the effective part 24a of the coil 24, which moves the movable part in a direction of Y-axis. The driving point exists on the plane of the coil 24, and is deviated from the optical axis of the objective lens 21. The driving point of the focusing coil is also formed similarly. Also, since magnetic flux is closed symmetrically to the center of the magnetic gap, no magnetic flux component generated outside a coil center for the coil 24 occurs, therefore, no force to rotate the movable part functions.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to an objective lens driving device for an optical pickup that projects a light spot onto an optical disk to perform recording and reproduction.

BACKGROUND ART FIG. 3 is an exploded perspective view showing the configuration of a conventional objective lens driving device. An objective lens 1 is fixed to a lens holder 2, and a focusing coil 3 and a tracking king coil 4, which are bonded and integrated, are attached to the lens holder 2.
The movable part is fixed to the through-hole part of the movable part. The four parallel wires 6 are connected to the base 5
Both ends are soldered to a base substrate 9 fixed to the lens holder 2 and a holder substrate 10 fixed to the lens holder 2, respectively. This allows the lens holder 2 to be supported in a cantilevered manner. A magnet 8 is fixed to a yoke 7, and the base 5, which is a fixed member, is attached to the yoke 7.
The inner yoke 7a facing the first magnet 8 provided on the yoke 7 enters the focus coil 3 with a gap. As a result, the lens holder 2
A portion of the focus coil 3 and tracking coil 4 attached to the holder can be inserted into the holder.

The focus coil 3 is wound so that its central axis is parallel to the optical axis of the objective lens 1, and when a current flows through it, the lens holder 2 moves in the optical axis direction (Z-axis direction in the figure). Further, the tracking coil 4 is wound as an effective part in the magnetic gap so that a current flows in the direction of the optical axis, and when the current flows, the lens holder 2 moves in a direction perpendicular to the optical axis (Y-axis direction in the figure). Moving. Here, a single magnetic circuit configuration is an essential condition for downsizing the objective lens driving device, and the driving points in the focusing direction and tracking direction are offset from the optical axis of the objective lens 1. As described above, the objective lens driving device drives the objective lens two-dimensionally in the optical axis direction and the direction perpendicular to the optical axis direction by passing a current through each coil.

Problems to be Solved by the Invention However, in the conventional example as described above, the movable part cannot be accurately driven in a direction perpendicular to the optical axis direction. Fourth
The figure is a perspective view (a) showing the principle of movement of the movable part in the direction perpendicular to the optical axis (Y-axis direction in the figure) by the tracking king coil 4 in this conventional example, and a plan view in the X-Y direction (
b).

The magnet 8 is fixed so that its north pole faces the inner yoke 7a. The arrow indicates the magnetic flux in the XY plane passing through the central axis of the tracking king coil 4, which was confirmed by actual measurement and computer simulation. In the effective portion 4a of the tracking king coil 4, current flows in the Z-axis direction to move the movable portion in the Y-axis direction. However, if we pay attention to the magnetic flux component extending outward from the center of the tracking king coil, a force is generated that moves the movable part in the X-axis direction. This magnetic flux is directed to the tracking king coil surface (Z-Y
It is observed in all directions away from the magnet on the plane). The tracking king coil consists of two sets of coils 4b and 4c, and these forces have a positive and negative relationship with respect to the X-axis direction, respectively. As a result, a force that rotates the movable part acts, making it impossible to accurately move the movable part in the direction perpendicular to the optical axis, and also buckling the wire 6 that supports the movable part, causing unnecessary resonance in the vibration system, which is fatal to servos. There is a problem that it becomes a defect.

In view of the above-mentioned conventional problems, the present invention provides an objective lens driving device that can stably drive an objective lens in the focusing and tracking directions.

Means for Solving the Problems In order to solve the above problems, the objective lens drive device of the present invention includes an objective lens that projects a light spot onto an optical disk;
a lens holder for holding the objective lens; a driving means for driving the objective lens and the lens holder in the focusing direction and the tracking direction; one end fixed to the fixing member and the other end fixed to the lens holder; The driving means includes a support member that supports the holder movably in the focusing direction and the tracking direction, and the driving means includes a focusing coil whose central axis is parallel to the optical axis of the objective lens, and a focusing coil whose central axis is parallel to the optical axis of the objective lens. It consists of a tracking king coil perpendicular to the magnetic field and a single magnetic circuit having a magnetic gap, and the driving point thereof does not coincide with the optical axis of the objective lens, and the magnetic gap has different S and N poles. It consists of a pair of magnets with opposing poles.

Effect By having the above configuration, it is possible to eliminate the magnetic flux component that flows outward from the center of the tracking king coil in the magnetic gap, eliminate the force that rotates the movable part, and achieve an objective lens drive device that provides accurate servo characteristics. .

EXAMPLE Hereinafter, an objective lens driving device of the present invention will be explained with reference to the drawings.

An embodiment of the present invention will be described using FIGS. 1 and 2. FIG. 1 is an exploded perspective view showing the configuration of an objective lens driving device in an embodiment of the present invention. The objective lens 21 is fixed to a lens holder 22, and a focusing coil 23 and a tracking king coil 24 are glued and integrated.
are fixed to the hollow part of the lens holder 22, and these constitute a movable part. The four parallel wires 26 are attached to a base substrate 29 fixed to the base 25.
and a holder substrate 30 fixed to the lens holder 22 at both ends. Thereby, the lens holder 22 is supported in a cantilevered manner. Two magnets 28 are fixed to the yoke 27 with their S and N poles facing each other with a gap, forming a single magnetic gap, and the base 25, which is a fixed member, is attached to the yoke 27. The focusing coil 23 is inserted into one of the magnets 28 and a part of the yoke to which this magnet is fixed, with a gap therebetween, so that the tracking king coil 24 is present in the magnetic gap. FIG. 2 is a perspective view (a) showing the principle of movement of the movable part in the direction perpendicular to the optical axis (Y-axis direction in the figure) by the tracking king coil 24 in this embodiment, and a plan view in the X-Y direction ( b). 2 magnets 2
8 is a yoke 27 with the N and S poles facing each other.
is fixed to. The arrow indicates the magnetic flux in the XY plane passing through the central axis of the tracking king coil 24, which was confirmed by actual measurement and computer simulation. In the effective part 24a of the tracking king coil 24,
Current flows in the Z-axis direction and moves the movable part in the Y-axis direction.

The driving point is on the surface of the tracking coil 24 and is offset from the optical axis of the objective lens 11. The same applies to the driving point of the focus coil. In addition, because the magnetic flux closes symmetrically with respect to the magnetic gap center, there is no magnetic flux component (Y-axis component) outward from the coil center for the tracking coil, which is located almost at the center of the magnetic gap, and no force to rotate the movable part acts on it. , it can be driven precisely in a direction perpendicular to the optical axis.

Effects of the Invention In the objective lens driving device of the present invention, as described above, the driving means includes a focusing coil whose central axis is parallel to the optical axis of the objective lens, and a tracking king whose central axis is perpendicular to the optical axis. Consisting of a coil and a single magnetic circuit having a magnetic gap, the driving point thereof is not aligned with the optical axis of the objective lens, and the magnetic gap causes different poles of S and N poles to face each other. Consisting of a pair of magnets, it eliminates the magnetic flux component that moves outward from the center of the tracking king coil in the magnetic gap, eliminates the force that rotates the moving part, and uses a simple configuration to accurately move the moving part perpendicular to the optical axis. It can be driven in various directions, resulting in better servo characteristics. Further, since leakage of magnetic flux to the outside of the magnetic gap can be suppressed and the magnetic flux can be concentrated within the magnetic gap, the driving efficiency of the tracking king coil and the focus coil is increased. As a result, each coil can be made lighter and smaller, and a compact and highly efficient objective lens driving device can be achieved. Furthermore, since leakage of magnetic flux to the outside can be suppressed, interference with metal parts such as a motor around the objective lens driving device and magnetic interference with other magnetic parts can be eliminated. In this way, a compact and high-performance objective lens driving device that can obtain accurate servo characteristics is realized.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view showing the configuration of an objective lens drive device in an embodiment of the present invention, and FIGS. 2(a) and (b) are relative to the optical axis of the movable part by the tracking king coil in the embodiment of the present invention. 3 is an exploded perspective view showing the configuration of the objective lens drive device in the conventional example, and FIGS. 4(a) and 4(b) are the tracking king in the conventional example. FIG. 2 is a perspective view and a plan view showing the principle of movement of a movable part by a coil in a direction perpendicular to the optical axis. 21...Objective lens, 22.O.Lens holder 2
3... Focus coil, 24... Tracking king coil, 25... Base, 26... Wire
27...Yoke, 28...Magnet, 29...
Base board, 30/holder board,

Claims (1)

[Claims] an objective lens for projecting a light spot onto an optical disk; a lens holder for holding the objective lens; a driving means for driving the objective lens and the lens holder in a focusing direction and a tracking direction; The support member has an end fixed to the lens holder and supports the lens holder movably in the focusing direction and the tracking direction, and the driving means has a coil whose central axis is parallel to the optical axis of the objective lens. It consists of a focusing coil, a tracking king coil whose center axis is perpendicular to the optical axis, and a single magnetic circuit having a magnetic gap, and the driving point thereof does not coincide with the optical axis of the objective lens. , the magnetic gap is S
An objective lens driving device comprising a pair of magnets having opposite poles and north poles facing each other.