JPS639307B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an apparatus for reading information by projecting successive light spots onto an information track recorded in a spiral or concentric form on a recording medium, for example, in which the information track and the information projected by an objective lens are used. The present invention relates to an objective lens driving device that drives an objective lens in a direction perpendicular to its optical axis and an information track in order to correct a relative positional deviation with a light spot, that is, a tracking error.

The above-mentioned information reading device is conventionally known, and a recording medium having an information track is, for example, called a video disk, and an encoded video signal or audio signal is transmitted through optical transmission characteristics, reflection characteristics, and phase characteristics. The optical information is read by rotating a video disc on which such optical information is recorded at high speed while focusing laser light emitted from a laser light source and projecting it onto the video disc. One of the features of such recording media is that the information recording density is very high, so that the width of each information track is very narrow and the spacing between successive information tracks is also very narrow. Therefore, the diameter of the reading light spot is also extremely small. In order to accurately read the original information from such a narrow information track in width and pitch, it is necessary to minimize the relative positional deviation between the reading light spot and the information track, that is, the tracking error. To this end, so-called tracking control has conventionally been performed in which the relative positional deviation between the reading light spot and the information track is detected, and the reading light spot is displaced in the width direction of the information track based on this tracking error signal. It is. As such a tracking mechanism, it has been proposed to arrange a vibrating mirror in the optical path between the laser light source and the objective lens, and to rotate this mirror in response to a tracking error signal. However, with such a tracking mechanism, it is difficult to obtain sufficiently satisfactory accuracy and response characteristics.

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, and the objective lens is moved perpendicular to its optical axis and the information track based on the tracking error signal. A method of displacement in the direction was proposed. In a drive device using such a leaf spring, possible methods for moving the objective lens include a method using an electromagnet, a voice coil method, and a method using a piezoelectric element, but in order to maintain good tracking response characteristics, It is necessary to make it small and lightweight. In an actual device, in addition to such tracking errors, there is also a focusing error in which the light spot is not correctly focused on the information track, and in order to correct this focusing error, the objective lens must be displaced in the direction of its optical axis. A focusing mechanism is also required. When the tracking mechanism is mounted on the focusing mechanism, the tracking mechanism needs to be small and lightweight in order to perform focusing correction well. Tracking mechanisms using electromagnets can provide the necessary force and are relatively easy to make compact and lightweight, but the relationship between the current flowing through the electromagnet coil and the displacement of the objective lens is non-linear, making it difficult to accurately track It is not possible to correct tracking errors. In addition, the voice coil method has drawbacks such as difficulty in reducing the size and weight, and devices using piezoelectric elements are difficult to obtain the necessary force.

The object of the present invention is to eliminate the various drawbacks mentioned above,
The objective lens can be moved linearly with respect to the tracking error signal, and the necessary force can be obtained sufficiently. Moreover, it can be made small and lightweight, and is especially useful for driving the objective lens two-dimensionally. The present invention aims to provide a suitable objective lens driving device.

The present invention provides an objective lens for correcting a relative positional deviation between an information track recorded spirally or concentrically on a recording medium and a reading light spot projected onto the recording medium by an objective lens, that is, a tracking error. In a device that drives a lens,
objective lens supporting means for movably supporting the objective lens in a direction perpendicular to the optical axis and the information track of the objective lens; and a movable member made of a permanent magnet that moves together with the objective lens or its holding frame;
By connecting first and second fixed yokes facing each other so as to sandwich the movable member in a direction perpendicular to the moving direction, and connecting the first and second fixed yokes at both ends thereof. a coupling portion made of a magnetic material disposed so as to surround the movable member; and first and second coils fixed to the first and second fixed yokes, respectively. By supplying a current corresponding to the tracking error signal representing the relative positional deviation to the coil of No. 2, the movable member made of the permanent magnet, and therefore the objective lens, is made perpendicular to its optical axis and the information track. This feature is characterized in that the tracking error is corrected by displacing it in a certain direction.

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

FIG. 1 shows the configuration and operating principle of an example of a driving means used in the objective lens driving device of the present invention. This driving means moves a movable member 1 made of a permanent magnet that moves together with the objective lens or its holding frame (both not shown) in a direction perpendicular to the optical axis of the objective lens and the information track as indicated by a double arrow A. First and second fixed yokes 2 and 2' are movably arranged and are arranged opposite to each other in a direction perpendicular to the moving direction A of the movable member 1.
and connecting members 3 and 3' made of magnetic material that connect both ends of these first and second fixed yokes 2 and 2', respectively, and First and second coils 4 and 4' are respectively wound to supply currents corresponding to tracking error signals.

According to such a configuration, since magnetic fields as shown by arrows B and B' are formed by the movable member 1 made of a permanent magnet, the first and second coils and the coils 4' that cross these magnetic fields When a current is passed through the portion in the direction indicated by the symbol in FIG. 1, a magnetic field is induced in the first and second yokes 2 and 2' in the direction indicated by arrow C. This magnetic field is in the same direction as one magnetic field B generated by the movable member 1 made of a permanent magnet, but in the opposite direction to the other magnetic field B'. Furthermore, when the direction of the current is reversed, this relationship is simply reversed, and the amount of magnetic flux passing through the movable member 1 becomes unrelated to the direction of the current flowing through the coils 4, 4'. Therefore, the current flowing through the coils 4, 4' and the amount of displacement of the movable member 1 have a linear relationship,
Furthermore, a sufficiently large amount of force can be obtained to drive the movable member 1.

FIGS. 2A and 2B show the construction of an example of an objective lens driving device according to the present invention using the driving means shown in FIG. 1. In this example, the lens holding frame 8 that holds the objective lens 7 is constructed with a permanent magnet.
corresponds to the movable member 1 shown in FIG. This lens holding frame 8 is suspended from fixing members 10 and 10' by a pair of leaf springs 9 and 9' constituting objective lens supporting means, and is suspended in the direction shown by arrow A in FIG. 2B, that is, the optical axis of the objective lens 7. and can be displaced in a direction perpendicular to the information track. The objective lens 7 is displaced in the direction shown by arrow A by passing a current corresponding to the tracking error through the first and second coils 4 and 4' wound around the first and second yokes 2 and 2'. Tracking errors can be corrected. In this example as well, as explained with reference to FIG. 1, the current flowing through the coils 4, 4' and the amount of displacement of the objective lens 7 have a linear relationship.

FIGS. 3A, 3B and 3C show the configurations of three other examples of objective lens driving devices according to the present invention. The objective lens driving device shown in FIG. 3A has the feature that the spaces between the lens holding frame 8 made of a permanent magnet and the first and second fixed yokes 2 and 2' are filled with magnetic fluids 11 and 11', respectively. This is the only difference from that shown in FIG. magnetic fluid 1
1 and 11', for example, Ferrofluidics'
Ferrofluid can be used. in this way,
If the gap between the lens holding frame 8 and the fixed yokes 2, 2' is filled with magnetic fluid 11, 11',
Since the magnetic fluids 11 and 11' continue to stably exist in the gap due to the strong magnetic field in the gap, their viscosity can produce a damping effect, making it possible to obtain good response characteristics. This has the advantage of increasing magnetic flux utilization efficiency.

The objective lens driving device shown in FIG. 3B does not use the connecting members 3, 3' as shown in FIG.
The first and second fixed yokes 2 and 2' are formed into an L-shape, and are brought together to form a closed magnetic circuit.

Furthermore, the objective lens driving device shown in FIG. 3C is
A closed magnetic circuit is constructed by integrally forming the first and second fixed yokes 2 and 2' without using the connecting members 3 and 3' as shown in FIG.

In addition, in FIGS. 3B and 3C, in order to obtain good damping characteristics, magnetism is applied between the lens holding frame 8 and the first and second fixed yokes 2 and 2', respectively, as in FIG. 3A. Can be filled with fluid.

FIGS. 4A and 4B show an objective lens driving device of the present invention that is capable of two-dimensionally displacing the objective lens both in the above-mentioned tracking error correction direction and in the direction of the optical axis of the objective lens, that is, in the focusing correction direction. This figure shows an example configuration.
The drive mechanism shown in FIG. 2 is used in this example.
A lens holding frame 8 that holds the objective lens 7 is made of a permanent magnet, and this lens holding frame 8 is supported by a pair of leaf springs 9.
and 9', it is attached to the protruding portion 12' of the middle frame 12. Therefore, the objective lens 7 is movable in the direction indicated by arrow A in FIG. 4A, that is, in the tracking error correction direction. The inner frame 12 is attached to the outer frame 14 by a pair of circular springs 13 and 13'. Therefore, the middle frame 12 is the objective lens 7.
It is also movable together with the holding frame 8 in the optical axis direction of the objective lens 7, that is, in the focusing correction direction. The first and second yokes 2 and 2' that cooperate with the lens holding frame 8 made of a permanent magnet, and the connecting members 3 and 3' that connect them are fixed to the outer frame 14 by suitable means (not shown). . Therefore, only the lens holding frame 8 is attached to the middle frame 12 that moves in the optical axis direction, resulting in a light weight. In order to perform focusing by displacing the middle frame 12 in the optical axis direction, a coil 16 is wound around a ring 15 provided integrally with the middle frame 12, and a permanent magnet 17 and yokes 18 and 1 that work together with the coil are wound.
9 to the outer frame 14.

According to such an objective lens driving device, it can be made small and lightweight, so that the objective lens 7 can be effectively moved in both the tracking error correction direction and the focusing correction direction, and in particular, it can move the objective lens 7 effectively in both the tracking error correction direction and the focusing correction direction. Regarding the movement in the direction, as described above, the first and second coils 4
Since the relationship between the current flowing through the lens 4' and the amount of movement of the objective lens 7 is linear, and sufficient force is obtained for the movement, accurate tracking error correction can be performed.

Note that the present invention is not limited to the above-mentioned example, and can be modified or changed in many ways. For example, in the objective lens drive device shown in FIG. 4, the drive mechanism shown in FIG. 2 is used, but the drive mechanism shown in FIGS. 3A, B, and C may also be used. Furthermore, by filling the space between the lens holding frame 8 and the first and second fixed yokes 2 and 2' with magnetic fluid, it is possible to obtain good damping characteristics in the focusing correction direction as well. . Furthermore, in addition to being directly attached to the outer frame 14, the drive mechanism is also attached to the yoke 1 for focusing.
The drive mechanism can be fixed using various mounting methods, such as mounting on the outer frame 14 via a spacer made of a material that does not allow magnetism to pass therethrough, or fixing by molding between the outer frame 14 and the drive mechanism. Furthermore, although the entire lens holding frame 8 is made of a permanent magnet, in the present invention, it is sufficient that a magnetic field is formed in a movable member such as the lens holding frame 8 in a direction perpendicular to the tracking error correction direction. The frame 8 may be made of a non-magnetic material, and a permanent magnet may be attached to a part of the frame 8 so that the above magnetic field is generated. Furthermore, the objective lens 7 can be supported movably in the tracking error correction direction by a single leaf spring without using the pair of leaf springs 9, 9'. Furthermore, the movable member made of a permanent magnet does not have to be used directly as a lens holding frame; for example, one end of an arm extending in the direction of movement of the movable member is fixed, and the objective lens is attached to the other end of this arm, detached from the closed magnetic circuit. Alternatively, the holding frame is fixed, one end of a leaf spring is attached to the objective lens or its holding frame on both sides or one side in the moving direction of the movable member, and the other end of the leaf spring is attached to the fixed member, and the objective lens is fixed. is supported movably in the tracking error correction direction, or one end of an arm extending in a direction perpendicular to the moving direction of the movable member is fixed, and the objective lens or The holding frame is fixed, one end of a leaf spring is attached to the objective lens or this holding frame on both sides or one side in the moving direction of the movable member, and the other end of the leaf spring is attached to the fixed member, and the objective lens is fixed. It can also be supported movably in the tracking error correction direction.

As described in detail above, according to the objective lens driving device of the present invention, the objective lens is moved by a predetermined amount in a predetermined direction by passing a current corresponding to the tracking error through the first and second coils. It is possible to obtain sufficient force for this movement, and it can be made small and lightweight, and is particularly effective for a mechanism that drives an objective lens two-dimensionally. Furthermore, since the relationship between the current flowing through the coil and the amount of movement of the objective lens is linear, tracking errors can be accurately corrected, and the objects of the present invention can be effectively achieved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the basic configuration and operation of an objective lens driving device according to the present invention, and FIGS. 2A and 2B are a front view and a plan view partially showing an embodiment of the objective lens driving device according to the present invention, as a cross section. Figures 3A, B and C are plan views respectively showing three other embodiments of the objective lens driving device according to the present invention, and Figures 4A and B are plan views of the objective lens driving device of the present invention which is driven two-dimensionally. FIG. 2 is a plan view and a front view showing an example of an objective lens driving device, with a portion thereof being shown in cross section. 1...Movable member made of a permanent magnet, 2...First
fixed yoke, 2'... second fixed yoke, 3,
3'... Connection member, 4... First coil, 4'...
Second coil, 7... Objective lens, 8... Lens holding frame, 9, 9'... Leaf spring, 10, 10'... Fixing member, 11, 11'... Magnetic fluid, 12... Middle frame , 13, 13'...Circular spring, 14...Outer frame,
16... Coil, 17... Permanent magnet, 18, 19
……yoke.

Claims (1)

[Claims] 1. Correcting the relative positional deviation between the information track recorded spirally or concentrically on the recording medium and the reading light spot projected onto the recording medium by the objective lens, that is, the tracking error. In a device for driving an objective lens, the objective lens supporting means movably supports the objective lens in a direction perpendicular to the optical axis of the objective lens and the information track, and moves integrally with the objective lens or its holding frame. A movable member made of a permanent magnet, first and second fixed yokes disposed opposite to each other so as to sandwich the movable member in a direction perpendicular to the moving direction, and between the first and second fixed yokes. a connecting portion made of a magnetic material and arranged to surround the movable member by connecting the movable member at both ends; and first and second coils fixed to the first and second fixed yokes, respectively. By supplying current corresponding to the tracking error signal representing the relative positional deviation to the first and second coils, the movable member made of the permanent magnet, and therefore the objective lens, is moved. 1. An objective lens drive device, characterized in that it is configured to correct tracking errors by displacing it in a direction perpendicular to an optical axis and an information track. 2 a first coil to which the first and second coils are fixed;
and a second fixed yoke is attached to the fixed member, the movable member consisting of the objective lens and a permanent magnet is attached together with the supporting means to a focusing mechanism that is displaced in the optical axis direction of the objective lens, and the objective lens is attached to the focusing mechanism that is displaced in the optical axis direction of the objective lens. 2. The objective lens driving device according to claim 1, wherein the objective lens driving device is capable of two-dimensional displacement in an optical axis direction and in a direction perpendicular to the optical axis and the information track. 3. Claim 1 or 2, characterized in that a space between the first and second fixed yokes and a movable member made of a permanent magnet is filled with magnetic fluid.
The objective lens drive device described.