JPS6187231A - Objective supporting device - Google Patents

Abstract

PURPOSE:To make the relation between driving force and the quantity of dis placement nearly linear and to perform accurate movement in a tracking direc tion by using an elastic member which is curved in a free state, and varying its curvature and allowing the movement in the tracking direction. CONSTITUTION:A holding cylinder 22 is coupled with a coil bobbin 25 through two leaf springs 23 and d24 which are curved circularly. Those two tracking leaf springs 23 and 24 do not curve at right angles to this paper surface, i.e. in an optical axis direction, so a lens 21 and the coil bobbin 25 moves as one body as to motion in said direction, i.e. focusing. The lens supported by the two circular leaf springs 23 and 24 are allowed to move in the tracking direction (X direction), but the leaf spring 23 and 24 in curved shapes vary in curvature in this case, so the relation between the driving force and the quantity of dis placement becomes nearly linear; tracking corrections are made excellently and the optical axis never slants during the tracking operation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a support device for an objective lens of an optical information reading device.

When reproducing a video disc or an audio disc on which information is optically recorded, it is necessary to perform focusing and tracking in order to correctly focus the reading light beam onto the information track on the disc surface. Since this focusing and tracking must be performed with very small amplitude and at high speed, the mechanism for performing these tasks becomes a problem.

Various proposals have been made regarding such a mechanism, but the most common one is to move the objective lens in the focusing direction for focusing, and to place a galvano mirror in the optical path of the reading beam for tracking. This is done by swinging the reading light beam in the tracking direction. However, in such a configuration, the reading light beam passes obliquely to the optical axis of the optical system such as the objective lens due to the tracking operation, so even in such a case, it is necessary to ensure that the light beam is focused correctly. In this case, it becomes necessary to use an optical system that does not have not only spherical aberration but also astigmatism, etc., which complicates the structure of the optical system and increases its weight, deteriorating the characteristics of the focusing control system.

In order to eliminate such drawbacks, it is possible to consider a method of configuring the optical system, especially the objective lens, so that the beam does not enter the optical system obliquely. In this case, it is important that the movement of the objective lens in the desired directions, the tracking direction and the focusing direction, is carried out correctly, and that these movements do not result in undesired movements in other directions.

Japanese Unexamined Patent Publication No. 51-61726 describes such an objective lens driving device. Figure 1 shows the plan view (
FIG. 2 shows a sectional view taken along the line AA' in FIG. 1. In the figure, the X direction is the track direction, and the Y direction is the track direction.
The direction is perpendicular to the track, and a deviation in the Y direction is a deviation from the track, so it is a tracking error, and a deviation in the X direction is a time deviation in the read signal, so it is called a time base error. I'll decide. The objective lens 1 is attached to a lens holder 2, and this holder 2 is attached to a frame 3 made of an elastic member.

Note that the reference numeral 4 indicates a side plate bridged over the frame 3.

The frame 3 is made of a magnetic material, and when an electric current is passed through electromagnets 5 or 5° disposed opposite to each other on the outside of the frame 3, a force is applied by this magnetic force. Since the frame 3 is fixed to the support 6.6', the entire frame does not move due to this force, but it bends as shown by the broken line in the figure, and the lens 1 moves in parallel in the Y direction. Note that a portion 7 within the frame 3 is filled with silicone rubber, silicone grease, etc. to function as a damper. Furthermore, if desired, the entire device for moving in the Y direction can be housed in a drive device for moving in the X direction with a similar configuration, so that tracking error correction and time base error correction can be performed. In FIG. 1, a configuration for moving the lens in the optical axis direction, that is, in the Z direction, for focusing is not shown. However, the above-mentioned publication describes that, for example, if a mechanism for this purpose is built into the lens holder 2, the lens 1 can be moved in the Z direction to adjust the focus.

However, in the structure shown in Figure 1, the support of frame 3 is 6゜6''.
Since the surfaces 8 and 8° attached to the lens 1 can also bend as shown by the two-dot chain line in the figure, the positioning of the lens 1 in the Y direction cannot be performed reliably. Therefore, undesired movement in the Y direction may occur with movement in the X direction for tracking correction, or movement in the Y direction may also occur due to external vibrations, resulting in time base errors. was there.

By increasing the width of the supports 6 and 6゛, it is possible to eliminate the deflection shown by the two-dot chain line of the frames 8 and 8゜, but this will limit the deformation of the frame in the desired direction, that is, the Y direction. You will end up being rejected. Because strut 6.6' is frame 3
A surface 9 that deforms as the lens 1 moves in the Y direction,
This is because they are provided at both ends of the 9.

Furthermore, if the driving device that moves in the Z direction for focusing is housed in the lens holder 2, the mass of the movable part that performs tracking will be large (this means that in order to perform good control, the entire device must be large). In other words, the amplitude of the movement for focusing needs to be about an order of magnitude larger than the movement for tracking, so the drive device for this must be large, and it is necessary to move it for tracking. It is unreasonable to configure the system to do this.

In addition, conventional support devices use linear leaf springs and bend them to move the objective lens in the tracking direction, but the relationship between the driving force and the amount of displacement deviates significantly from the linear relationship. , Accurate tracking correction is difficult.

SUMMARY OF THE INVENTION An object of the present invention is to provide an objective lens support device in which the relationship between driving force and displacement amount is approximately linear, and tracking correction can be performed accurately.

The present invention provides a device that supports an objective lens for optically reading information recorded on a recording medium so as to be movable in a tracking direction perpendicular to its leading axis, in which the objective lens has a curved shape. The objective lens is connected to the base by an elastic support member, and is configured so that the objective lens can be moved in the tracking direction by changing the curvature of the elastic support member. The invention will now be described in detail with reference to the drawings.

FIG. 3 is a sectional view showing one embodiment of the objective lens support device according to the present invention, taken along a plane perpendicular to the optical axis. 4 is a sectional view taken along line BB' in FIG. 3. The objective lens 21 is attached to a cylindrical holding tube 22. The holding cylinder 22 is connected to the coil bobbin 25 by two circularly curved leaf springs 23,24. Since these two tracking leaf springs 23 and 24 do not bend in the direction perpendicular to the plane of FIG. 3, that is, in the direction of the optical axis, the lens 21 and the coil bobbin 25 move integrally in this direction, that is, regarding focusing. A coil 26 is wound around the coil bobbin 25, and magnets 27 are arranged to sandwich the bobbin 25 from the inside and outside. Further, the coil bobbin 25 is attached to the frame 31 that supports the magnet 27, for example, by spiral focusing.
It is held by a leaf spring 32. Therefore, when current is applied to the coil 26, the bobbin 25 and the lens holding cylinder 22 move together in the optical axis direction, and this movement can be controlled by the current applied to the coil 26. Focusing can be performed with such a configuration. Next, a mechanism related to tracking will be explained.

There are two electromagnets 3 facing each other on the inner surface of the inner cylindrical portion 28 of the magnet.
3.33° is attached, and when a current is passed through one of these, the magnetic force generated by this acts on the lens holding cylinder 22 made of a magnetic material, attracts it, and as a result, the circular leaf springs 23 and 24 are attached. The curvature changes, and the lens holding cylinder 22 moves in the direction perpendicular to the optical axis, BB". Tracking control can then be performed by controlling the current flowing through the electromagnet 33 or 33. Tracking and focusing are controlled based on tracking errors and focusing signals detected by some method.

According to the above configuration, two circular leaf springs 23, 2
The lens supported by the curved leaf spring 2 can move in the tracking direction (X direction).
Since the curvature of 3.24 is changed, the relationship between the driving force and the amount of displacement becomes almost linear, and suitable tracking correction can be performed, and the optical axis does not tilt due to tracking.

Note that the present invention is not limited only to the above-described embodiments. Many other variations are possible for the spring mechanism that supports the objective lens. FIG. 5 (al is a view of an example viewed from the optical axis direction; semicircular leaf springs 83 and 83' are used to move the objective lens holding cylinder 22 not only in the tracking direction but also in the time base direction. Supported example, (bl shows another example viewed from the direction perpendicular to the optical axis; semicircular leaf spring 103.103° is used to support the objective lens holding cylinder 22 so that it can move in the focusing direction and the tracking direction. This is an example.

In FIG. 5, the broken line arrow indicates the direction in which the lens moves.

According to the present invention, an elastic member that is curved in a free state is used and its curvature is changed to enable movement in the tracking direction, so the relationship between the driving force and the amount of displacement can be made almost linear, and the tracking It is possible to move in a certain direction accurately. Also, as shown in Figure 5,
If the support mechanism is movably supported not only in the tracking direction but also in a direction perpendicular to the tracking direction, the structure of the support mechanism can be simplified.

[Brief explanation of drawings]

Fig. 1 is a plan view showing the configuration of an example of a conventional objective lens driving device, Fig. 2 is a sectional view taken along the optical axis of Fig. 1, and Fig. 3 is a plan view showing the configuration of an example of a conventional objective lens driving device. A cross-sectional view of one embodiment taken along a plane perpendicular to the optical axis, Figure 4 is Figure 3B.
5 is a diagram showing a modification of the objective lens support device of the present invention. 21...Objective lens 22...Lens holding tube 23, 24...Circular plate spring 25 for tracking
・Coil bobbin 27...Magnet 32...Focusing plate spring 33.33'...Tracking electromagnet 83.83''
, 103.103' ... Semicircular leaf spring for tracking Fig. 3 Fig. 4? 1252El 26 Figure 5 (a) (b)

Claims (1)

[Claims] 1. In a device that supports an objective lens for optically reading information recorded on a recording medium so as to be movable in a tracking direction perpendicular to its optical axis, the objective lens is made of an elastic material having a curved shape. What is claimed is: 1. An objective lens support device, characterized in that it is connected to a base by a support member, and is configured such that the objective lens can be moved in a tracking direction by changing the curvature of the elastic support member.