JPS6243256B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved objective lens support device in an objective lens drive device used in a video disc playback device or the like.

In a video disk reproducing apparatus, it is necessary to perform focusing so that the reading light beam is properly focused on the disk surface, and to perform tracking so that the light beam follows the track on the disk. In this case, after obtaining the focusing and tracking signals by an appropriate method,
One problem is how to drive the lens system based on these signals. In many conventional methods, a galvanometer mirror is placed in the optical path of the reading light beam to tilt the light beam for tracking. For this reason, the tracking operation causes the light beam to pass obliquely to the optical axis of the optical system such as the objective lens, so in order to properly focus the light beam even in such cases, it is necessary to use a spherical surface. It is necessary to remove not only aberrations but also astigmatism and the like, which makes designing the optical system difficult. Therefore, the optical system becomes complicated, and especially when the objective lens is large and heavy, it is difficult to provide good frequency characteristics and damping characteristics to the control system that drives the objective lens for focusing, and the disadvantage is that the driving device becomes large. It was hot.

Therefore, there is a proposal to perform tracking by moving the light beam parallel to the optical axis of the optical system without tilting it. For this purpose, it is sufficient to configure the objective lens so that it can be moved in a plane perpendicular to the optical axis, but if the movement of the objective lens for focusing, that is, movement in the direction of the optical axis is also included, the objective lens can be moved along the optical axis. This means that a configuration for driving in a plane perpendicular to the optical axis and in the direction of the optical axis is required. Japanese Unexamined Patent Publication 1973-
Publication No. 61726 has a description regarding such an objective lens driving device. FIG. 1 shows a plan view (a view seen from the optical axis direction), and FIG. 2 shows a cross-sectional view taken along line A-A' in FIG. In the figure, the X direction is the track direction, and the Y direction is a direction perpendicular to the track. A deviation in the y direction is a deviation from the track, so it is a tracking error, and a deviation in the Since this is a time difference, we will call it a time base error. 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 a current is passed through an electromagnet 5 or 5' disposed opposite to the outside of the frame 3, a force is generated by this magnetic force. Since the frame 3 is fixed to the supports 6 and 6', the entire frame 3 is not moved by this force, but the flexible lens 1 is moved in parallel in the Y direction as shown by the broken line in the figure. Note that the portion 7 inside the frame 3 is filled with silicone rubber, silicone grease, etc. to make it move as a damper.
Furthermore, if desired, the entire apparatus for moving in the Y direction can be housed in a drive apparatus for moving in the X direction having 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. But the first
In the structure shown in the figure, the surfaces 8, 8' attached to the supports 6, 6' of the frame 3 can also flex as shown by the chain lines in the figure, so that the lens 1 can be reliably positioned in the Y direction. Not possible. For this reason, undesired movement in the X direction may occur as a result of movement in the Y direction for tracking correction, or movement in the X direction may also occur due to external vibrations, resulting in time base errors. There were some drawbacks. By widening the width of the supports 6, 6', it is possible to eliminate the deflection of the frames 8, 8' as shown by the dashed lines, but this will limit the deformation of the frames in the desired direction, that is, the Y direction. This will result in This is because the supports 6, 6' are provided at both ends of the surfaces 9, 9' which deform as the lens 1 of the frame 3 moves in the Y direction. Further, the conventional objective lens support device for tracking has a disadvantage that the structure is complicated and expensive.

An object of the present invention is to maintain a constant distance between the recording medium and the objective lens and the distance between the objective lens and the fixed member even when the objective lens is driven in the tracking direction, so that the structure can be maintained without fluctuations in the objective lens in the focusing direction and the tangential direction. The object is to provide an extremely simple objective lens support device.

The present invention relates to an objective lens driving device that drives an objective lens in a tracking direction perpendicular to both the lens optical axis direction and the information track direction using electromagnetic driving means in order to read information recorded in a track shape on a recording medium. , at least two elastic support members arranged in a plane perpendicular to the lens optical axis and at point-symmetric positions with respect to the lens optical axis, and extending along a direction perpendicular to the tracking direction. It is characterized in that one end of each is fixed to a fixing member and the other end is fixed to an objective lens.

An embodiment of the present invention will be described below based on the drawings.

FIG. 3 is a sectional view showing an example of a lens driving device for focusing and tracking according to the present invention, taken along a plane perpendicular to the optical axis. Also the fourth
The figure 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 has two leaf springs 2
3 and 24 to a fixed member, for example, a coil bobbin 25. The holding cylinder 22 or the two leaf springs 23 and 24 are made of magnetic material. 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. The inner cylindrical portion 28 of the magnet 27 has holes 29 and 30 through which the leaf springs 23 and 24 pass through, and the coil bobbin 25
The coil bobbin 25 is attached to a frame 31 supporting the magnet 27 by a focusing leaf spring 32 (the shape of which is shown in FIG. 8, for example). It is held in place. Therefore, when a current is applied to the coil 26, the bobbin 25 and the lens holding tube 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.

Two electromagnets 33, 33' are attached to the inner surface of the inner cylindrical portion 28 of the magnet, facing each other, and the magnetic force generated by passing a current through one of these acts on, for example, the leaf springs 23, 24 made of magnetic material. These objects are attracted, and the lens holding cylinder 22 moves in the direction perpendicular to the optical axis, ie, in the direction BB'. So electromagnet 3
Tracking control can be performed by controlling the current flowing through 3 or 33'. Of course, these tracking and focusing controls are performed based on tracking errors and focusing signals detected by some method.

According to the above configuration, two leaf springs 23,
The lens supported by 24 can only move in the tracking direction (Y direction) in a plane perpendicular to the optical axis, and cannot move in other directions, such as the X direction, so that suitable tracking correction can be performed. can.

In another embodiment of the present invention, a piezoelectric element is attached to a tracking leaf spring (reference numerals 23 and 24 in Figure 3), and the deformation of the leaf spring and therefore the amount of movement of the lens is detected from the piezoelectric element and used in the control system. Some devices are designed to perform good tracking control by applying feedback. FIG. 5 shows an example in which such a configuration is applied to the embodiment shown in FIGS. 3 and 4, and for the sake of clarity, C-C in FIG.
A cross-sectional view taken along C' is shown. Except for the piezoelectric element 41 attached to the leaf spring 23, the third
It has the same configuration as the embodiment shown in FIGS.

In addition, the piezoelectric element attached to the leaf spring that supports such a lens is not only used to detect the amount of displacement of the leaf spring, but also a tracking signal is added to the piezoelectric element and used to displace the leaf spring. Tracking can also be performed using a piezoelectric element instead.

Next, an example of a method for obtaining a tracking signal will be described. FIG. 6 shows this, and leaf springs 43 and 44 (Fig. 3 leaf springs 23 and 2
4) A signal having a constant amplitude and frequency is applied to the piezoelectric element 45 attached to the piezoelectric element 45 to cause the lens 42 to vibrate minutely in the tracking direction. Then, the light comes out from the light source 46, is reflected by the disk surface 47, and is reflected by the polarizing prism 48.
The information read out by the light receiver 49 through the optical system is modulated by the above-mentioned frequency. FIG. 7a shows the modulation of information read out by the light receiver 49 during normal tracking.Since the minute vibrations are centered around the track, the amplitude and period of the modulation are almost constant. becomes. As shown in FIG. 7b, when the tracking becomes deviated, the modulation amplitude changes and its period also changes, so a signal indicating a tracking error can be extracted from this information.

FIG. 8 shows another embodiment of the invention. This also basically has the same structure as that explained in FIGS. 3 and 4. FIG. 8a is a top view, and FIG. 8b is a sectional view taken along the optical axis. A coil bobbin 53 is supported by a leaf spring 51 (corresponding to the leaf spring 32 in FIG. 4) and a leaf spring 52, and a lens 56 and a lens barrel 57 are attached to two leaf springs 54 and 55 attached to the bobbin 53. is installed. By providing the focusing leaf springs at two locations above and below the lens holding tube 57, the lens optical axis is prevented from tilting when the lens holding tube 57 moves in the optical axis direction. Furthermore, in this embodiment, the coil bobbin 53 is extended downward so that the coil 58 is wound around it, and the magnet 59 is placed across this part, so that a plate is attached to the inner cylinder part of the magnet as in the above-mentioned embodiment. There is no need to provide a hole for the spring to pass through. Note that the tracking electromagnets 60 and 61 are provided facing each other with the lens holding cylinder 57 in between and used for tracking, as in the above embodiment.

In both the embodiment shown in FIG. 3 and the embodiment shown in FIG. 8, the two tracking leaf springs are placed at symmetrical positions with respect to the optical axis, and the focusing leaf springs are also symmetrical with respect to the optical axis. . For this reason, undesired vibrations are less likely to occur despite the structure in which the vibration system consisting of the moving part for tracking is mounted on the vibration system in the optical axis direction consisting of the movable part for focusing and the vibration system consisting of the movable part for tracking in the direction perpendicular thereto.

The present invention is not limited to the above-described embodiments; for example, the leaf spring for focusing is not limited to a spiral shape as shown in the drawings, but may be a simple rectangular leaf spring.

Furthermore, in the above-described embodiment, the focusing plate spring and the coil bobbin can be relatively rotated to prevent the coil bobbin from slightly rotating around the optical axis during focusing. Moreover, the shape of the focusing leaf spring can be made into an appropriate shape so that the coil bobbin does not rotate with the focusing operation. Also, the point at which the leaf spring for tracking is attached to the lens holding member is not limited to the ends of the diameter of the lens in the tracking direction, or on an extension thereof, as in the embodiment. 72 and 73 may be attached. Furthermore, when a piezoelectric element is attached to a leaf spring and used as a driving source or for detecting the amount of displacement of the leaf spring, the piezoelectric element is not necessarily attached to one side of the leaf spring, but may be attached to both sides.

The objective lens support device in the tracking drive device of the present invention is such that even when the objective lens is driven in the tracking direction, the distance between the recording medium and the objective lens and the distance between the objective lens and the fixed part of the elastic support member are constant. Therefore, when driving such a lens,
This has the effect that the objective lens does not change at all in the focus direction and the tangential direction. Furthermore, since the elastic support member extends in a direction perpendicular to the optical axis, it is possible to arrange a detection system optical member such as a prism close to the objective lens, thereby realizing a thinner optical pickup.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of a conventional objective lens driving device, FIG. 2 is a sectional view of the same conventional driving device, and FIG. 4 is a sectional view taken along the vertical plane, FIG. 4 is a sectional view taken along FIG. 3 B-B', and FIG. 5 is a sectional view taken along FIG. 3 C--
6 is a diagram showing an example of a method for extracting a tracking signal; FIG. 7 is a diagram showing an example of a tracking signal obtained by the configuration shown in FIG. 6; 8a and 8b are diagrams showing the structure of another embodiment of the present invention, and FIG. 9 is a diagram showing another example of a tracking leaf spring attached to a lens holder. 21...Objective lens, 22...Lens holding cylinder,
23, 24... Tracking leaf spring, 25...
Coil bobbin, 26... Coil, 27... Magnet, 3
2...Focusing leaf spring, 33, 33'...
...Electromagnet, 41...Piezoelectric element, 43, 44...Tracking leaf spring, 45...Piezoelectric element, 49...
... Light receiver, 51, 52 ... Tracking leaf spring, 53 ... Coil bobbin, 54, 55 ... Focusing leaf spring, 57 ... Lens holding tube, 7
2,73...Tracking leaf spring.

Claims (1)

[Claims] 1. An objective that drives an objective lens in a tracking direction perpendicular to both the lens optical axis direction and the information track direction by electromagnetic driving means in order to read information recorded in a track shape on a recording medium. In the lens driving device, at least two lenses are disposed in a plane perpendicular to the lens optical axis and at point-symmetrical positions with respect to the lens optical axis, and extend along a direction perpendicular to the tracking direction. An objective lens support device characterized in that one end of each elastic support member is fixed to a fixing member and the other end is fixed to an objective lens.