JPH03141041A - Objective lens driving device - Google Patents

Abstract

PURPOSE:To always obtain a stable control characteristic by providing a ring- like position damper in the periphery of a bearing line in axial symmetry centering around the axial center of a sliding bearing mechanism between a movable part containing a movable body and a coil bobbin, and a still part. CONSTITUTION:A ring-like positioning damper member 38 is provided symmetrically even against the surface positioned on a line for connecting the center of an objective lens 28 and an axial center and on the axial center, therefore, when a movable plate 25 is displaced in the focus direction, component in the tracking direction of the damper members 38 opposed by inserting and holding the symmetrical surface can be balanced. Accordingly, a crosstalk in the focus direction and the tracking direction can be reduced, the more stable servo-control in two directions can be realized. Also, by giving the symmetric property by using one ring-like damper member 38, it can be prevented that the crosstalk increases.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to an objective lens driving device, and particularly to an objective lens driving device suitable for being incorporated into an optical disc record playback device.

(Prior Art) In recent years, in the field of audio equipment, digital recording and reproducing methods using PCM (Pulse Code Modulation) technology are becoming popular. As is well known, the PCM digital recording and reproducing system has the advantage that the audio characteristics are not affected by the characteristics of the recording medium and that it is very resistant to noise. For recording media intended for disks, optical, electrostatic, mechanical, and other reproduction methods are already known. No matter which of these playback methods is adopted, the playback device is required to have advanced functions and performance not found in conventional analog methods.

For example, in an optical disc record playback device that uses a CD (compact disc) system among optical playback systems, it is necessary to accurately read information that is precisely recorded on a disc at a track pitch of 1.6 μm. For this reason, the reading system must have advanced functions and performance.

However, optical disc record playback devices generally employ a method of reading information recorded on a disc through an objective lens. In this case, to achieve good playback, the focus of the objective lens must always be on the group or pit where information is recorded on the disc, and the objective lens must be focused so that the track does not deviate from the track where information is recorded. It is necessary to precisely control the position. For this reason, generally, the objective lens is held by an objective lens drive device, and the drive device is controlled by a servo system using read information signals, thereby performing focusing control and tracking control. .

By the way, the main parts of the objective lens driving device that performs the above-described focusing control and tracking control are normally constructed as shown in FIGS. 4 to 6.

That is, a shaft 2 is implanted in the center of the upper surface of a base 1 made of a magnetic material, and is fitted with the shaft 2 to form the shaft 2.
A holding cylinder 4 formed in the shape of a cylinder with a bottom is attached via a bearing cylinder 3 constituting a sliding bearing mechanism so as to be slidable in the axial direction and rotatable around the axis. The objective lens 5 is supported by the so-called bottom wall 4a of the holding tube 4, and the cylindrical portion 4b of the holding tube 4 is used as a coil bobbin. A tracking coil 7 for controlling the position around the axis is fixed.

In addition, two inner yokes 8a and 8b are arranged symmetrically about the axis 2 so as to fit into the cylindrical portion 4b in a non-contact manner at a position facing the inner surface of the bottom wall 4a of the holding cylinder 4 on the upper surface of the base 1. Further, the inner yoke 8a is provided on the outside of the cylindrical portion 4b.
outer yokes 9a, respectively, in a relationship facing the outer surface of 8b;
9b and these outer yokes 9a, 9b and the base 1.
A permanent magnet 10 magnetized in the axial direction is interposed between the upper surface of the magnet and the upper surface of the magnet. Further, a small shaft 11 is provided upright on the upper surface of the base 1 and at a position facing the inner surface of the bottom wall 4a of the holding cylinder 4, and between this small shaft 11 and the bearing cylinder 3 there is provided a small shaft 11 formed of, for example, rubber. Damper member 1 for setting neutral position in tracking direction
2 is interposed. In addition, 13 in Fig. 5 is the base 1.
A light transmission hole is shown that is provided in and guides light to and from the objective lens 5.

The objective lens drive device configured as described above changes the position of the holding cylinder 4 in the Y-axis direction in FIG. This objective lens driving device had the following problems. That is, the damper member 12, which determines the neutral position of the holding cylinder 4, is mounted at approximately the same position as the focusing coil 6 and the tracking coil 7 in the Y-axis direction. When the damper member 12 is mounted at such a low position, most of the weight of the holding tube 4 including the objective lens 5 will be placed on the upper part of the damper member 12, making the support of the holding tube 4 unstable. turn into. As shown in FIG. 8, even if the central axis of the holding cylinder 4 coincides with the direction of gravity, the central axis of the holding cylinder 4 is inevitably inclined.

When driving the objective lens 5 in the focusing direction using such an objective lens driving device, holding 1! ! 4 and the shaft 2, a so-called twisting phenomenon occurs. Moreover, since most of the weight of the holding cylinder 4 acts on the twisted part, it becomes very difficult to pull it in during servo control, and the high-speed and high-precision positioning of the objective lens 5 requires a large amount of quasi-static displacement in the direction of the coarse scrap. The relationship between force and force has a hysteresis characteristic as shown in FIG. Since the quasi-static displacement has such a large hysteresis, there is a problem in that it is difficult to pull in the servo when applying it. Conventionally, this problem has been solved by increasing the surface accuracy of the bearing mechanism, but there is a limit to increasing the surface accuracy, and the reality is that no fundamental solution has been reached. be.

(Problems to be Solved by the Invention) The present invention has been made in view of the above circumstances, and its purpose is to suppress the hysteresis characteristic in the relationship between the quasi-static displacement in the focus direction and the force. Therefore, it is an object of the present invention to provide an objective lens drive device with a simple structure, which can contribute to the facilitation of retraction in servo control, and whose characteristics can always be stably obtained.

[Object of the Invention] (Means for Solving the Problems) The present invention supports a movable body that supports an objective lens with a sliding bearing mechanism that allows sliding in the axial direction and rotation around the axis, and also provides a mechanism for supporting the movable body. In the objective lens driving device, the movable body and the coil bobbin are provided with a coil bobbin that supports a part of an electromagnetic drive element that applies force in the ring direction and around the axis, and is provided on the movable body concentrically with the axis of the sliding bearing mechanism. A positioning damper member is provided between the movable part including the stationary part and the stationary part, and is formed in a ring shape that is axially symmetrical about the axis of the sliding bearing mechanism and goes around the axis. The damper member is located at a position farther from the objective lens with respect to the axis.

Further, the positioning damper member is formed to be plane symmetrical with respect to a plane located on a line connecting the axially symmetrical positions and on the axial center line.

(Function) Since the positioning damper members are arranged symmetrically around the axis, even if displacement in the focus direction is applied,
Since the damper members facing each other across the axis generate and balance moments about the orthogonal axes in opposite directions, the normal force applied to the sliding bearing mechanism does not increase. Therefore, the hysteresis characteristic is suppressed, and it is possible to facilitate pull-in during servo control. In addition, by arranging the damper member plane symmetrically with respect to the plane located on the line connecting the axially symmetrical positions and on the axial center line, it is possible to prevent crosstalk caused by displacement in the tracking direction when displaced in the focus direction, or vice versa. Crosstalk can be reduced and servo control can be made more stable. Furthermore, since the damper member is configured in a ring shape that goes around the axis, it is easy to form a damper member with good symmetry, and as a result, hysteresis characteristics can be further suppressed.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view of an objective lens driving device according to an embodiment of the present invention, FIG. 2 is a view taken along the line C--C in FIG.
FIG. 3 is a partially cutaway perspective view of the same device.

In these figures, reference numeral 21 indicates a base made of magnetic material and formed, for example, in the shape of a disk. A hole 22 is provided approximately in the center of the base 21, and inner yokes 23a and 2 symmetrically arranged on the upper surface of the base 21 are arranged around the hole 22.
3b is provided to protrude upward. And the inner yoke 23a.

A shaft 24 is disposed between the holes 23b, and the lower end of the shaft 24 is inserted into the hole 22 and fixed with screws or other appropriate means.

A flat movable plate 25 made of, for example, a non-magnetic material is attached to the shaft 24. The movable plate 25 is formed in a symmetrical shape with respect to the center position, and the movable plate 25 is approximately The sliding bearing has a bearing cylinder 26 in the center thereof, which is fitted with the shaft 24 to form a mechanism. The movable plate 25 is mounted so that it can freely slide in the axial direction by fitting the bearing sleeve 26 and the shaft 24 and can freely rotate around the shaft. A hole 27 is provided at one end in the longitudinal direction of the movable plate 25, as shown in FIG.
Fixed. Further, at the other end of the movable plate 25 in the longitudinal direction, at a position symmetrical to the mounting position of the objective lens 28 with the shaft 24 as the center, there is a movable plate 25 including a coil and a coil bobbin, which will be described later, as also shown in FIG. A counterweight 2 for aligning the center of gravity of the entire part with the axial center line of the shaft 24
9 is fixed.

The surface of the movable plate 25 facing the base 21 has an inner yoke 23a having the inner diameter described above.

The fill bobbin 30 is fixed concentrically with the shaft 24 and is formed into a cylindrical shape, the diameter of which is larger than the distance between the outer surfaces of the shaft 23b (and whose outer diameter is smaller than twice the distance between the ring center line of the shaft 24 and the objective lens 28). This coil bobbin 30 can also be formed integrally with the movable plate 25 when the movable plate 25 is formed.A focusing coil 31 is wound around the outer peripheral surface of the coil bobbin 30, and Two sets of tracking coils 32 are fixed at symmetrical positions on the outer peripheral surface.

On the other hand, at a position outside the coil bobbin 30, an outer yoke 33a faces each of the inner yokes 23a and 23b via the coil bobbin 30.

33b is arranged, and these outer yokes 33a, 3
Permanent magnets 34a and 34b magnetized in the axial direction are interposed between 3b and the base 21, respectively. and,
The outer yoke 33a and the permanent magnet 34a are connected by bolts 35 made of non-magnetic material, and the outer yoke 33b and the permanent magnet 3
4b are each fixed to the base 21 by bolts 36 made of non-magnetic material. This fixing can also be done using adhesive.

Thin supporting plates 37a and 37b each having the same shape are fixed symmetrically to the lower surface of both ends of the movable plate 25 in the longitudinal direction with the shaft 24 as the center. and,
At the same position on the lower surfaces of the support plates 37 a and 37 b, two positions 180 degrees apart in the circumferential direction of a damper member 38 formed in a ring shape that goes around the axis are fixed via adhesive or the like. . The damper member 38 is formed by punching or molding a thin silicone rubber plate, and is fixed as described above on the line connecting the center of the objective lens 28 and the axis of the shaft 24 and on the axis. The structure is such that a plane-symmetrical shape is formed with respect to a plane located at . The damper member 38 is fixed to the outer yokes 33a, 33b via fixing mechanisms 39a, 39b at the center position in the circumferential direction between the support plates 37g, 37b. The fixing mechanisms 39a and 39b are applied to the upper end surfaces of the outer yokes 33a and 33b, respectively, and are applied to a spacer 40 having a groove P in the upper surface into which a part of the damper member 38 is fitted, and the upper surface of this spacer 40. A backing plate 41, and screws 42 that integrally fix the backing plate 41, spacer 40, and damper member 38 to each outer yoke 33a, 33b with a part of the damper member 38 fitted into the groove P. It is configured.

Furthermore, when the objective lens driving device of the present invention is viewed from the Y-axis direction, the damper member 38 is arranged at approximately the same position as the objective lens 28 and the counterweight 29. The focusing coil 31 and tracking coil 32 are designed to be mounted below the damper member 38.

With such a configuration, the movable plate 25 is moved in the X-axis direction in FIG. 7 by the electromagnetic force accompanying the control of energization to the focusing coil 31, thereby performing focusing control and controlling the energization to the tracking coil 32. The movable plate 25 is rotated in the X-axis direction in FIG. 7 by the electromagnetic force accompanying this, and tracking control is performed thereby.
It has the following advantages:

That is, since the positioning damper members 38 are arranged symmetrically with respect to the axis, even if the movable plate 25 is displaced in the focus direction, the damper members 38 facing each other with the shaft 24 in between
The substantial damper portions generate opposite moments about the orthogonal axes that cancel each other out, and eventually the moments about the orthogonal axes become zero. Therefore, the bearing [26 is not tilted and pressed against the pongee 24, and the hysteresis characteristic between the force applied in the focus direction and the quasi-static displacement can be sufficiently controlled. As a result, it is possible to facilitate pull-in in servo control.

As seen in the hysteresis characteristics shown in Figure 4, the solid line shows the case when a conventional cantilever-supported damper member is used, whereas the broken line shows the case when a ring-shaped damper is used as in this example. It can be seen that the hysteresis characteristics are greatly improved. In addition, what is shown by the -dotted chain line is
This is a hysteresis characteristic when a cantilevered damper member is provided closer to the objective lens than the center of gravity of the movable part.

Furthermore, since the positioning damper member 38 is provided symmetrically with respect to the plane located on the line connecting the center of the objective lens 28 and the axial center line and on the ring center line, the movable plate 25 can be displaced in the focus direction. At this time, the component forces in the tracking direction of the damper members 38 facing each other across the plane of symmetry can be balanced. Therefore, crosstalk between the focusing direction and the tracking direction can be reduced, and stable servo control in two directions can be realized.

Furthermore, when forming a symmetrical damper structure with two or more damper members, if the damper members are made of rubber such as silicone, the hardness may vary depending on molding conditions such as temperature and humidity during molding. This causes variations in the stiffness of each damper member, which causes the moment of the opposing damper members and the component force in the tracking direction to become unbalanced, increasing the hysteresis between the force and the quasi-static displacement, and increasing the stiffness in the focus direction. and crosstalk in the tracking direction increases. but,
In this embodiment, one ring-shaped damper member 38 is used to create symmetry, so the above problem can be solved, and an objective lens driving device with extremely suppressed hysteresis characteristics can be obtained. Can be done.

Note that the present invention is not limited to the embodiments described above. That is, it goes without saying that the present invention can also be applied to the holding cylinder type shown in FIG. Further, the damper member may be attached to any position on the movable part as long as the above-mentioned conditions are satisfied. Also,
A shaft may be provided on the movable side and a bearing sleeve may be provided on the stationary side.

[Effects of the Invention] As explained above, according to the objective lens driving device of the present invention, the so-called twisting phenomenon between the movable body and the shaft can be minimized, making it easy to pull in the servo control, resulting in always stable control. characteristics will be obtained.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the main parts of an objective lens driving device according to an embodiment of the present invention, FIG. 2 is a view taken along the line C--C in FIG. FIG. 4 is a perspective view of the main parts of a conventional objective lens drive device, FIG. 5 is a cutaway view taken along line A-A in FIG. 4, and FIG. B-B line cut arrow view, 7th
The figure is a diagram for explaining problems with the conventional device. 5... Movable plate 6... Bearing tube 8... Objective lens 9... Counter weight 0... Coil bobbint... Focusing coil 2... Tracking coils 3a, 33b... Outer yoke 4a, 34b... Permanent magnets 7a, 37b... Support plate 8... Damper members 9a, 39b... Fixing mechanism

Claims (3)

[Claims] (1) Part of an electromagnetic drive element that supports the movable body that supports the objective lens with a sliding bearing mechanism that allows sliding in the axial direction and rotation around the axis, and also applies forces in the axial direction and around the axis to the movable body. In the objective lens driving device, a coil bobbin supporting the slide bearing mechanism is provided on the movable body concentrically with a ring center line of the slide bearing mechanism, and the slide bearing mechanism is disposed between the movable part including the movable body and the coil bobbin and the stationary part. A positioning damper member formed in a ring shape that goes around the axis symmetrically with respect to the axis is provided, and the positioning damper member is located at a position farther from the objective lens with respect to the axis. An objective lens driving device characterized in that the objective lens driving device is arranged at. (2) The positioning damper member is formed in a ring shape that goes around the axis symmetrically with respect to the axis of the sliding bearing mechanism. The objective lens driving device according to item 1. (3) The positioning damper member is formed in plane symmetry with respect to a plane located on a line connecting axially symmetrical positions and on a ring center line. The objective lens drive device described.