JPH0670856B2 - Objective lens drive - Google Patents

Description

Description: [Object of the Invention] (Field of Industrial Application) The present invention relates to an objective lens driving device, and more particularly to an objective lens driving device suitable for being incorporated in an optical disc record reproducing device.

(Prior Art) In recent years, in the field of audio equipment, a digital recording / reproducing system using a PCM (Pulse Code Modulation) technique is becoming widespread. As is well known, the PCM digital recording / reproducing system has advantages such that the audio characteristic is not influenced by the characteristic of the recording medium and that it is very strong against noise. When a recording medium intended for a disk is used, its reproducing system is already known such as an optical system, an electrostatic system and a mechanical system. Regardless of which of these reproduction methods is adopted, the reproduction apparatus is required to have a high level of function and performance not found in the conventional analog method.

For example, in the optical disc record reproducing apparatus of the CD (Compact Disc) type among the optical reproducing systems, it is necessary to accurately read the information recorded precisely on the disc with a track pitch of 1.6 μm. For this reason, the reading system must have sophisticated functions and performance.

Therefore, the optical disc record reproducing apparatus generally adopts a method of reading information recorded on the disc through an objective lens. In this case, in order to realize good reproduction, the objective lens is always focused on the group or pit where the information of the disk is recorded, and the track of the objective lens is adjusted so that the track does not deviate from the track where the information is recorded. The position needs to be finely controlled. Therefore, in general, the objective lens is held by the objective lens driving device, and the driving device is controlled by the servo system using the read information signal, thereby performing focusing control and tracking control. .

By the way, the main part of the objective lens driving device for performing the focusing control and the tracking control as described above is usually configured as shown in FIGS. 4 to 6.

That is, the shaft 2 is planted in the center of the upper surface of the base 1 made of a magnetic material, and the shaft 2 is fitted to the shaft 2 to form a slide bearing mechanism with the shaft 2 to form a bottomed cylinder. The holding cylinder 4 formed in a shape is mounted so as to be slidable in the axial direction and rotatable about the axis. A focusing coil for supporting the objective lens 5 on the so-called bottom wall 4a of the holding barrel 4 and utilizing the tubular portion 4b of the holding barrel 4 as a coil bobbin for controlling the axial position on the outer periphery of the tubular portion 4b. 6 and a tracking coil 7 for controlling the position around the axis are fixed. Further, the two inner yokes 8a, 8b are symmetrical with respect to the shaft 2 in such a manner that the two inner yokes 8a, 8b are fitted in a non-contact manner in the cylindrical portion 4b 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. And the outer yokes 9a and 9b are arranged outside the cylindrical portion 4b so as to face the outer surfaces of the inner yokes 8a and 8b, respectively, and between the outer yokes 9a and 9b and the upper surface of the base 1. An axially magnetized permanent magnet 10 is interposed between the two. In addition, on the upper surface of the base 1 and the holding cylinder 4
1. A small shaft 11 is erected at a position facing the inner surface of the bottom wall 4a of the above, and a neutral direction setting damper member 12 made of, for example, rubber is interposed between the small shaft 11 and the bearing cylinder 3. I am letting you. Incidentally, reference numeral 13 in FIG. 5 denotes a light transmission hole provided in the base 1 for guiding light to and from the objective lens 5.

The objective lens driving device thus configured changes the position of the holding barrel 4 in the Y-axis direction in FIG. 4 by the electromagnetic force associated with the energization control of the focusing coil 6, however, is configured as described above. Further, the conventional objective lens driving device has the following problems. That is, the damper member 12, which determines the neutral position of the holding cylinder 4, has its mounting position in the Y-axis direction substantially the same as that of the focusing coil 6 and the tracking coil 7. When the damper member 12 is mounted at such a low position, most of the weight of the holding cylinder 4 including the objective lens 5 is placed above the damper member 12, so that the support of the holding cylinder 4 becomes unstable. turn into. Then, 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 inevitably tilts.

When the objective lens driving device is used to drive the objective lens 5 in the focusing direction, a so-called twisting phenomenon occurs between the holding cylinder 4 and the shaft 2. Moreover, since most of the weight of the holding cylinder 4 acts on the twisted portion, it becomes very difficult to pull in the servo control, and high-speed and high-accuracy positioning of the objective lens 5 is large and quasi-static displacement in the sparse dust direction is large. The relationship between force and force has a hysteresis characteristic as shown in FIG. As described above, since the quasi-static displacement has a large hysteresis, there is a problem that it is difficult to pull in the servo. Therefore,
In order to solve such a problem, conventionally, the surface precision of the bearing mechanism has been increased, but there is a limit to increasing the surface precision, and the fact is that a fundamental solution has not been reached.

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

[Object of the Invention] (Means for Solving the Problems) The present invention relates to a movable body that supports an objective lens, a sliding bearing mechanism that allows the movable body to slide in the axial direction and rotate about the axis, and A coil bobbin that is a part of the movable body and is provided around the axis of the sliding bearing mechanism and allows passage of magnetic flux, and a coil supported by the coil bobbin for driving at least the movable body in the axial direction. In an objective lens driving device having and, so as to go around the axial center line in an axially symmetric relationship about the axial center line of the slide bearing mechanism, and at a position farther from the objective lens with respect to the axial center line, It is characterized in that a ring-shaped positioning damper member having a curved portion is arranged.

(Operation) Since the positioning damper members are symmetrically arranged about the axis, even if displacement in the focus direction is given,
Since the damper members facing each other across the axial line generate counterbalanced moments about the orthogonal axes, the normal force applied to all the bearing mechanisms does not increase. Therefore, the hysteresis characteristic is suppressed, and pull-in during servo control can be facilitated. In addition, by disposing the damper member in plane symmetry with respect to the planes located on the line connecting the axially symmetrical positions and the axial center line, crosstalk that is displaced in the tracking direction when displaced in the focus direction, or vice versa. Crosstalk can be reduced, and servo control can be more stabilized. Further, since the ring-shaped damper member is arranged at a position farther than the objective lens, the movable body can be stably hung as compared with the case where the damper member is fixed near the center of the movable body. Therefore, the inclination of the movable body with respect to the axis, that is, the twisting phenomenon of the movable body can be suppressed to the minimum, and the pull-in in the servo control in the focusing direction can be facilitated and the control characteristics can be stabilized.

(Example) Hereinafter, an example of the present invention will be described 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 sectional view taken along the line CC in FIG.
Further, FIG. 3 is a perspective view showing the device with a part thereof cut away.

In these figures, reference numeral 21 denotes a magnetic material, for example, a disk-shaped base. A hole 22 is provided substantially in the center of the base 21, and the hole 22 is formed on the upper surface of the base 21.
Inner yokes 23a and 23b are provided symmetrically and projecting upward with respect to the center. A shaft 24 is arranged between the inner yokes 23a and 23b, and the lower end side of the shaft 24 has the hole.
It is inserted in 22 and fixed by screwing or other suitable means.

The movable plate 25, on which the movable plate 25 formed of, for example, a non-magnetic material is formed flat, is attached to the shaft 24. The movable plate 25 is formed in a symmetrical shape with respect to the center position. A bearing cylinder 26 that fits with the shaft 24 and constitutes a sliding bearing mechanism is provided at the center. The movable plate 25 is mounted so that it can be freely slipped in the axial direction and rotatable about the axis by fitting the bearing tube 26 and the shaft 24 together. As shown in FIG. 3, a hole 27 is provided at one end of the movable plate 25 in the longitudinal direction, and the objective lens 28 uses this hole 27 to set its optical axis as an axis.
It is fixed to the movable plate 25 in parallel with 24. At the other end of the movable plate 25 in the longitudinal direction, at a position symmetrical with respect to the mounting position of the objective lens 28 about the axis 24, a movable member including a coil and a coil bobbin, which will be described later, is also provided as shown in FIG. A counterweight 29 for fixing the center of gravity of the entire portion to the axis of the shaft 24 is fixed.

Then, on the surface of the movable plate 25 facing the base 21,
The coil bobbin 30 formed in a cylindrical shape has an inner diameter larger than the distance between the outer surfaces of the inner yokes 23a and 23b and smaller than twice the distance between the axis of the shaft 24 and the objective lens 28. It is fixed concentrically with. This coil bobbin 30
Can also be formed integrally with the movable plate 25 when forming the movable plate 25. 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, the coil bobbin is located outside the coil bobbin 30.
Outer yokes 33a, 33b are arranged so as to face the inner yokes 23a, 23b via the respective outer yokes 30, and a permanent magnet 34a magnetized in the axial direction is provided between the outer yokes 33a, 33b and the base 21. , 34b are respectively interposed. And
The outer yoke 33a and the permanent magnet 34a are bolts 35 made of a non-magnetic material.
The outer yoke 33b and the permanent magnet 34b are fixed to the base 21 by bolts 36 made of a non-magnetic material. This fixing can also be fixed using an adhesive.

Then, thin support plates 37a and 37b formed in the same shape are symmetrically fixed to the lower surfaces of both ends in the longitudinal direction of the movable plate 25 at positions farther from the objective lens 28 about the axis 24. . And, at the same position on the lower surface of the support plates 37a, 37b, a damper member formed in a ring shape that makes one turn around the axis
Two positions, which are different by 180 degrees in the circumferential direction of 38, are fixed via an adhesive or the like. The damper member 38 is formed by punching or molding a thin silicon rubber plate, and on the line connecting the center of the objective lens 28 and the shaft center line of the shaft 24 in the fixed state as described above and on the shaft center line. It is configured so that a plane-symmetrical shape is formed with respect to the surface located at. The damper member 38 is attached to the support plate 37.
It is fixed to the outer yokes 33a and 33b via fixing mechanisms 39a and 39b at the center position in the circumferential direction between a and 37b. Fixing mechanism 39
The a and 39b are applied to the upper end surfaces of the outer yokes 33a and 33b, respectively, and a spacer 40 having a groove P into which a part of the damper member 38 is fitted, and a contact plate applied to the upper surface of the spacer 40. 41, the contact plate 41, the spacer 40, and the tamper member in a state where a part of the damper member 38 is fitted in the groove P.
And a screw 42 for integrally fixing 38 to each outer yoke 33a, 33b.

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

With such a structure, the movable plate 25 is moved in the Y-axis direction in FIG. 7 by the electromagnetic force associated with the energization control of the focusing coil 31, whereby the focusing control is performed and the tracking coil is moved. Although the movable plate 25 is rotated in the X-axis direction in FIG. 7 by the electromagnetic force associated with the energization control to 32, and the tracking control is performed by this, there is the following advantage.

That is, since the positioning damper member 38 is arranged symmetrically with respect to the axis, even if the movable plate 25 is displaced in the focus direction, a substantial damper portion of the damper member 38 that faces the shaft 24 is opposed. Generate opposite moments about the orthogonal axis and cancel each other out, and eventually the moment about the orthogonal axis becomes zero. Therefore, the bearing cylinder 26 is not inclined and pressed against the shaft 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 pulling in the servo control. As can be seen from the hysteresis characteristics shown in FIG. 4, the solid line showing the case where the conventional cantilever-supported damper member is used is shown by the broken line when the ring-shaped damper is used as in this embodiment. It can be seen that the hysteresis characteristics are greatly improved. The one-dot chain line shows the hysteresis characteristic when the cantilevered damper member is provided closer to the objective lens than the center of gravity of the movable portion.

Further, the damper member 38 is fixed to the support plates 37a, 37b formed at a position farther than the objective lens 28. Therefore, as compared with the case where the damper member 38 is fixed near the center of the movable plate 25, the movable plate 25 can be suspended and supported more stably. Therefore, the inclination of the movable plate 25 with respect to the shaft 24, that is, the so-called twisting phenomenon of the bearing tube 26 can be suppressed to a minimum, and the pull-in in the servo control in the focusing direction can be facilitated and the control characteristics can be stabilized.

Further, since the positioning damper member 38 is provided symmetrically with respect to the line connecting the center of the objective lens 28 and the axis and the plane located on the axis, the movable plate 25 is displaced in the focus direction. At this time, it is possible to balance the component forces in the tracking direction of the damper members 38 that face each other across the symmetry plane. Therefore, crosstalk in the focusing direction and the tracking direction can be reduced, and more stable servo control in two directions can be realized.

Furthermore, in the case where the symmetrical damper structure is formed by two or more damper members, if the damper member is made of rubber such as silicone, it will be greatly affected by molding conditions such as temperature and humidity during molding. The hardness changes and rigidity variations occur in each damper member.This causes the momentum of the opposing damper members and the component force in the tracking direction to be unbalanced, increasing the hysteresis between the force and the quasi-static displacement. Or, there will be more crosstalk in the focusing and tracking directions. However, in this embodiment, since the one ring-shaped damper member 38 is used to provide the symmetry, the above problems can be solved, and the objective lens driving device in which the hysteresis characteristic is extremely suppressed is provided. Obtainable.

The present invention is not limited to the above embodiment. That is, it goes without saying that the present invention can be applied to the holding cylinder type shown in FIG. Further, if the mounting position of the damper member on the movable side satisfies the above-mentioned conditions, the damper member may be mounted on any of the movable parts. Further, the shaft may be provided on the movable side and the bearing tube may be provided on the stationary side.

[Effects of the Invention] As described above, according to the objective lens driving device of the present invention, the so-called twisting phenomenon between the movable body and the shaft is suppressed to a minimum, so that the pull-in in the servo control becomes easy and the stable control is always performed. The characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view showing a main part of an objective lens driving device according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line CC in FIG. 1, and FIG. FIG. 4 is a perspective view with a cutaway view, FIG. 4 is a perspective view of a main part in a conventional objective lens driving device, FIG. 5 is a sectional view taken along the line AA in FIG. 4, and FIG. BB line cutting arrow view, 7th
The figure is a diagram for explaining the problems of the conventional device. 21 …… base 23a, 23b …… inner yoke 24 …… axis 25 …… movable plate 26 …… bearing tube 28 …… objective lens 29 …… counterweight 30 …… coil bobbin 31 …… focusing coil 32 …… tratz King coil 33a, 33b …… Outer yoke 34a, 34b …… Permanent magnet 37a, 37b …… Support plate 38 …… Damper member 39a, 39b …… Fixing mechanism

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akiya Goto 72 Horikawa-cho, Sachi-ku, Kawasaki-shi, Kanagawa Stock company Toshiba Horikawa-cho factory (56) Reference JP-A-57-92441 (JP, A) Actual Kaisho 58-62448 (JP, U)

Claims (1)

[Claims] 1. A movable body that supports an objective lens, a slide bearing mechanism that allows the movable body to slide in the axial direction and rotate around the axis, and a shaft of the slide bearing mechanism that is a part of the movable body. In the objective lens drive device, a coil bobbin provided around a core wire for allowing passage of magnetic flux, and a coil supported by the coil bobbin for driving at least the movable body in an axial direction, A ring-shaped positioning damper having a curved portion formed so as to go around the axial center line in a symmetrical relationship about the axial center line of the mechanism and at a position farther from the objective lens with respect to the axial center line. An objective lens driving device, in which members are arranged.