JP2602004B2 - Objective lens drive - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention 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. 2. Description of the Related Art In recent years, in the field of audio equipment, a digital recording / reproducing system using a PCM (pulse code modulation) technique has been spreading. As is well known, the PCM digital recording / reproducing method has advantages such as that the audio characteristics are not affected by the characteristics of the recording medium and that they are very strong against noise. As a recording medium for a disk, an optical type, an electrostatic type, a mechanical type, and the like are already known as a reproducing system. Regardless of which of these playback systems is employed, the playback device is required to have advanced functions and performance not found in the conventional analog system. [0003] For example, in an optical disc record reproducing apparatus based on a CD (compact disc) system among optical reproducing systems, a disc has a track pitch of 1.6.
It is necessary to accurately read information that is precisely recorded in μm. For this reason, the reading system must have advanced functions and performance. However, an optical disc record reproducing apparatus generally employs a method of reading information recorded on a disc via an objective lens. In this case, in order to realize good reproduction, the objective lens is always focused on the groove or pit where the information of the disc is recorded, and the objective lens is not shifted from the track where the information is recorded. The position needs to be finely controlled. Therefore, generally, the objective lens is held by an objective lens driving device, and the driving device is controlled by a servo system using the read information signal, thereby performing focusing control and tracking control. The main part of the objective lens driving device for performing the focusing control and the tracking control as described above is usually constructed as shown in FIGS. More specifically, a shaft 2 is implanted at the center of the upper surface of a base 1 formed of a magnetic material, and is fitted to the shaft 2 to form a sliding bearing mechanism together with the shaft 2. A holding cylinder 4 formed in a cylindrical shape with a bottom is mounted so as to be able to slide in the axial direction and to be rotatable around the axis via the base 3. The so-called bottom wall 4a of the holding cylinder 4 supports the objective lens, and uses the cylindrical part 4b of the holding cylinder 4 as a coil bobbin, and a focusing coil 6 and a shaft for controlling the axial position on the outer periphery of the cylindrical part 4b. The tracking coil 7 for controlling the position in the turning direction is fixed. The two inner yokes 8a and 8b are symmetrical about the axis 2 in such a manner that the two inner yokes 8a and 8b are fitted into 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 without contact. And the inner yoke 8 is provided outside the cylindrical portion 4b.
a and 8b are opposed to the outer surfaces of the outer yokes 9 respectively.
a, 9b, and these yokes 9a, 9b and the base 1
A permanent magnet 10 that is magnetized in the axial direction is interposed between the upper surface and the upper surface. Further, a small shaft 11 is erected 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 is formed of, for example, rubber or the like between the small shaft 11 and the bearing cylinder 3. Damper member 1 for setting neutral position in tracking direction
2 is interposed. In FIG. 5, reference numeral 13 denotes a light transmission hole provided on the base 1 for guiding light to the objective lens 5 and light from the objective lens 5. In the objective lens driving device thus configured, the position of the holding cylinder 4 is changed in the Y-axis direction in FIG. 4 by the electromagnetic force accompanying the energization control of the focusing coil 6, thereby performing the focusing control. At the same time, the position of the holding cylinder 4 is rotated in the X-axis direction in FIG. 4 by the electromagnetic force associated with the energization control of the tracking coil 7, thereby performing the tracking control.
These energization controls are performed by a servo system (not shown). [0008] However, the conventional objective lens driving device constructed as described above has the following problems. That is, the damper member 12 which determines the neutral position of the holding cylinder 4 is moved with the objective lens 5
It is to be fixed at the position opposite to. As described above, since the damper member 12 is fixed to the stationary portion at a position away from the center of the holding cylinder 4 to one side, a moment about the orthogonal axis is generated in the holding cylinder 4 when a displacement is given in the focus direction. . For this reason, a reaction force proportional to the moment is generated in the sliding bearing mechanism that restricts rotation about the orthogonal axis. Since the sliding friction of the sliding bearing mechanism is almost proportional to the normal force, the larger the displacement in the focusing direction, the larger the frictional force acts. Therefore, the relationship between the quasi-static displacement in the focus direction and the reaction 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, measures have been taken by increasing the surface accuracy of the bearing mechanism.However, there is a limit to increasing the surface accuracy, and in fact, it has not been fundamentally solved. is there. The present invention has been made in view of such circumstances, and an object of the present invention is to suppress a hysteresis characteristic in a relation between a quasi-static displacement in a focusing direction and a force, thereby facilitating pulling in servo control. It is another object of the present invention to provide an objective lens driving device capable of always obtaining stable control characteristics. In order to achieve the above object, the present invention provides a movable body supporting an objective lens, and allows the movable body to slide in the axial direction and rotate around the axis. A sliding bearing mechanism, a coil bobbin that is a part of the movable body and is provided around an axis of the sliding bearing mechanism, and that allows a magnetic flux to pass therethrough, and that at least the movable body supported by the coil bobbin is axially An objective lens driving device having a coil for driving the movable member and the movable portion including the movable body and the coil bobbin and a stationary portion, and further away from the objective lens about an axis of the slide bearing mechanism as a center. At least two axially symmetric positions are curved in a plane perpendicular to the axis so as to be plane-symmetric with respect to a line connecting the positions and a plane located on the axis. A positioning damper member provided with a portion is provided. According to the present invention constructed as described above, since the damper member is arranged symmetrically with respect to the axis, even if a displacement in the focus direction is given, the damper member faces the axis. The matched dampers generate a moment about the opposite orthogonal axis to balance. For this reason, the normal force applied to the slide bearing mechanism can be reduced, and the hysteresis characteristics can be suppressed. Therefore, it is possible to contribute to facilitation of servo pull-in. In addition, since the damper member is provided in plane symmetry with respect to a plane located on a line connecting the two axially symmetric positions and an axis line, crosstalk displaced in the tracking direction when displaced in the focus direction. , Or vice versa, can be reduced, which can further contribute to the stability of servo control. Further, the damper member has a curved portion, and the movable portion and the stationary portion are connected via this portion. Therefore, when the movable body makes a sliding displacement in the axial direction or a rotational displacement around the axis, an excessive restoring force is not generated on the movable body by the damper member, and the relationship between the displacement amount of the movable body and the electromagnetic driving force is not generated. Can be kept substantially linear, and servo control can be easily performed. Further, since the damper member is disposed at a position farther than the objective lens, the displacement amount of the damper member with respect to the predetermined rotation amount of the movable body is smaller than when the damper member is fixed near the center of the movable body. Can be increased.
Therefore, the damping function of the damper member can be sufficiently exhibited. 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 one embodiment of the present invention, FIG. 2 is a sectional view taken along the line CC in FIG. 1, and FIG. 3 is a partially cutaway view of the device. It is a perspective view. In these figures, reference numeral 21 denotes a magnetic material, for example, a base formed on a flat plate. Base 2
1 is provided with a hole 22 at a substantially central portion thereof.
Inner yokes 23a and 23b are provided on the upper surface of 1 so as to project symmetrically with the hole 22 as a center. A shaft 24 is disposed between the inner yokes 23a and 23b. The lower end of the shaft 24 is inserted into the hole 22 and fixed by screws or other appropriate means. The shaft 24 is provided with a movable plate 25 made of a non-magnetic material and formed flat. The movable plate 25 is formed in a symmetrical shape with the center position as a boundary, and has a bearing cylinder 26 that is fitted to the shaft 24 to form a slide bearing mechanism at a substantially central portion thereof. And
The movable plate 25 is mounted so as to be free to slide in the axial direction by fitting the bearing cylinder 26 and the shaft 24 and to be rotatable around the shaft. FIG. 3 shows one end of the movable plate 25 in the longitudinal direction.
The objective lens 28 is fixed to the movable plate 25 with its optical axis parallel to the axis 24 by using the hole 27 as shown in FIG. In addition, 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 about the axis 24, a movable part including a coil and a coil bobbin, which will be described later, as shown in FIG. A counterweight 29 for fixing the entire center of gravity to the axis of the shaft 24 is fixed. On the surface of the movable plate 25 facing the base 21, the inner yokes 23a, 2
A coil bobbin 30 formed in a cylindrical shape that is larger than the distance between the outer surfaces of 3b and whose outer shape is smaller than twice the distance between the axis of the shaft 24 and the objective lens 28 is fixed concentrically with the shaft 24. The coil bobbin 30 can 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, the inner yokes 23a, 23a are located outside the coil bobbin 30 via the coil bobbin 30.
outer yokes 33a, 33b
Are disposed between the outer yokes 33a and 33b and the base 21, and permanent magnets 34 magnetized in the axial direction are provided.
a and 34b are interposed respectively. The outer yoke 33a and the permanent magnet 34a are made of a nonmagnetic material bolt 35.
The outer yoke 33b and the permanent magnet 34b are fixed to the base 21 by bolts 36 made of a nonmagnetic material. This fixation can also be fixed using an adhesive. At both ends of the movable plate 25 in the longitudinal direction (positions farther than the objective lens 28), symmetrical positions with respect to the axis of the shaft 24 are provided via thin metal plates 37a and 37b. Damper member 38 for setting the neutral position
a, 38b are fixed at one end. The other ends of these damper members 38a, 38b are thin metal plates 39a,
Posts 40a, 4 erected on base 21 via 39b
0b. The damper members 38a, 38b
For example, punch out a thin rubber plate and
A curved portion is formed in a square frame shape. One of two opposing sides is fixed to the movable plate 25, the middle part of the other side is fixed to the support, and the objective lens 28 They are arranged in a plane-symmetric relationship with respect to a line connecting the center and the axis of the shaft 24 and a plane located on the axis. Further, the damper members 38a, 38b are bent in a plane perpendicular to the axis (the plane shown in FIG. 1). With such a configuration, the movable plate 25 is moved in the Y-axis direction in FIG. 3 by the electromagnetic force accompanying the energization control of the focusing coil 31, thereby performing the focusing control and the tracking coil 32. Although the movable plate 25 is rotated in the X-axis direction in FIG. 3 by the electromagnetic force accompanying the energization control to the motor and the tracking control is performed by this, there are the following advantages. That is, since the damper members 38a and 38b for positioning the movable plate 25 are arranged symmetrically with respect to the axis of the shaft 24, the movable plate 25 is displaced in the Y-axis direction which is the focus direction. Also, the damper members 38a and 38b facing each other with the shaft 24 as a boundary generate a moment about the opposite orthogonal axis and cancel each other. Therefore, the moment about the orthogonal axis becomes zero. For this reason, the bushing 2
As a result, the hysteresis characteristic of the relation between the force applied in the focus direction and the quasi-static displacement can be suppressed. Therefore, it is possible to contribute to facilitation of servo pull-in, and eventually, the above-described effects can be obtained. In the case of the embodiment, the damper member 38
Since a and 38b are provided in plane symmetry with respect to a line connecting the axis and the center of the lens and a plane located on the axis, when the movable plate 25 is displaced in the focus direction, the movable plate 25 faces the symmetry plane. The component forces in the tracking direction of the entire corresponding damper member are balanced. For this reason, crosstalk between the focus direction and the tracking direction can be reduced, which can contribute to more stable two-way servo control. Further, the damper members 38a and 38b are formed with a curved portion in a rectangular frame shape, and the movable portion and the stationary portion are connected via this portion. Therefore, when the movable body makes a sliding displacement in the axial direction or a rotational displacement about the axis, no excessive restoring force is generated on the movable body by the damper members 38a and 38b, and the displacement of the movable body with respect to the electromagnetic driving force is prevented. The relationship between the quantities can be kept substantially linear, and servo control can be easily performed. In the present invention, in particular, the damper member 38
a and 38 b are arranged at positions farther than the objective lens 28. Therefore, the displacement amount of the damper members 38a, 38b with respect to the predetermined rotation amount of the movable plate 25 can be increased as compared with the case where the damper members 38a, 38b are fixed near the center of the movable plate 25. Therefore, the damping function of the damper members 38a and 38b can be sufficiently exhibited. The present invention is not limited to the embodiment described above. That is, it goes without saying that the present invention can be applied to the holding cylinder type shown in FIG. Further, the shape and material of the damper member are not particularly limited. The mounting position on the movable side of the damper member may be mounted at any position on the movable portion as long as the above-described conditions are satisfied. Further, a shaft may be provided on the movable side and a bearing cylinder may be provided on the stationary side. As described above, according to the present invention, since the damper member is arranged symmetrically with respect to the axis, even if a displacement in the focus direction is given, the damper member faces the axis. The matched dampers generate a moment about the opposite orthogonal axis to balance. For this reason, the normal force applied to the slide bearing mechanism can be reduced, and the hysteresis characteristics can be suppressed. Therefore, it is possible to contribute to facilitation of servo pull-in. In addition, since the damper member is provided in plane symmetry with respect to a plane located on a line connecting the two axially symmetric positions and on an axis line, crosstalk displaced in the tracking direction when displaced in the focus direction. , Or vice versa, can be reduced, which can further contribute to the stability of servo control. Further, the damper member has a curved portion, and the movable portion and the stationary portion are connected via this portion. Therefore, when the movable body makes a sliding displacement in the axial direction or a rotational displacement around the axis, an excessive restoring force is not generated on the movable body by the damper member, and the relationship between the electromagnetic driving force and the displacement amount of the movable body is not generated. Can be kept substantially linear, and servo control can be easily performed. Further, since the damper member is disposed at a position farther than the objective lens, the displacement amount of the damper member with respect to the predetermined rotation amount of the movable body is smaller than when the damper member is fixed near the center of the movable body. Can be increased.
Therefore, the function of the damper member can be sufficiently exhibited.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a main part of an objective lens driving device according to one embodiment of the present invention. FIG. 2 is a sectional view taken along line CC in FIG. 1; FIG. 3 is a perspective view showing the device in a partially cutaway manner. FIG. 4 is a perspective view of a main part of a conventional objective lens driving device. FIG. 5 is a sectional view taken along line AA in FIG. 4; FIG. 6 is a sectional view taken along the line BB in FIG. 4; FIG. 7 is a diagram for explaining a problem of the conventional device. [Description of Signs] 21 ... Bases 23a, 23b ... Inner yoke 24 ... Shaft 25 ... Movable plate 26 ... Bearing cylinder 28 ... Objective lens 29 ... Counterweight 30 ... Coil bobbin 31 ... Focusing coil 32 ... Tracking coils 33a, 33b ... Outer yoke 34a, 34b ... permanent magnets 38a, 38b ... damper members

Claims (1)

(57) [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 to rotate around the axis, and a part of the movable body. A coil bobbin provided around the axis of the slide bearing mechanism, which allows passage of magnetic flux; a coil supported by the coil bobbin for driving at least the movable body in the axial direction; and a magnetic flux applied to the coil. And a magnet that supplies
Objective lens Oite the driving device, the movable member and at least two movable parts that between a and distant axisymmetric than the objective lens around the shaft center line of the sliding bearing mechanism of a stationary portion including said coil bobbin having a A position damper member having a curved portion formed in a plane perpendicular to the axis so as to be plane-symmetric with respect to a line connecting the positions and a plane positioned on the axis. An objective lens driving device, which is provided.