JP2693143B2 - 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. Recently, in the field of audio equipment, a digital recording / reproducing system utilizing a PCM (pulse code modulation) technique has emerged and is becoming widespread in order to achieve as high a fidelity as possible. In other words, this is what is called digital audio conversion, and it is in principle that the audio characteristics do not depend on the characteristics of the recording medium and are markedly superior to those of the conventional analog method. This is because it has been established. In this case, a recording medium intended for a disk (disc) is called a DAD system, and reproduction systems such as an optical type, an electrostatic type and a mechanical type are known. Even if any of these reproducing methods is adopted, it is required that a reproducing apparatus that reproduces the reproducing method can satisfy various advanced functions and performances that are not found in conventional reproducing apparatuses. It It is, for example, C in the optical reproduction system.
In an optical disc record reproducing device of the D (compact disc) type, a diameter formed by depositing a metal thin film for forming pits (unevenness with different reflectance) corresponding to digital (PCM) data on a transparent resin disc. 12c
An optical disc of m and 1.2 mm in thickness is driven by a CLV (constant linear velocity) system at a variable rotation speed of about 200 to 500 rpm. In this case, since this disc has a track pitch of 1.6 μm and has recorded a huge amount of information capable of performing stereo reproduction for about 1 hour on one side, various advanced functions and performances are required. It is easy to nod. In the above-mentioned optical disc record reproducing apparatus, what is next required is that each mechanical section can be reliably operated with an organic and simple structure without waste.
In addition to further miniaturization, it is necessary to make further improvements such as power saving measures for reducing power consumption. By the way, an objective lens driving device is given as one of the concrete objects of such a request. In an optical disc reproducing apparatus, a focusing and tracking servo for moving an objective lens so as to follow (the focus is always on a groove or pit where a signal is recorded and is not deviated from a track where a signal is recorded). Need to call. There is a shaft sliding type as an objective lens driving mechanism therefor. As shown in FIGS. 5 and 6, a conventional shaft sliding type lens driving device has a lens mounted in a bobbin 2 which is free to rotate and slide around an axis 1, and the objective lens 3 is a bobbin 2. Is rotated around the axis 1 to move in the tracking direction (arrow A in the figure), and the bobbin 2 slides with respect to the axis 1 to move in the focusing direction (arrow B in the figure). The damper 4 for determining the neutral position of the bobbin is the shaft 1.
It is attached at a position symmetrical to the objective lens 3 with the lens sandwiched therebetween. As described above, since the damper 4 is fixed to the bobbin 2 at a position away from the center of the damper, when a displacement is applied in the focus direction, a moment around the axis A in the figure is generated.
Therefore, a reaction force proportional to the moment is generated in the bearing portion that restricts the rotation around the arrow A axis. Since the sliding friction of the bearing portion is almost proportional to the vertical drag force, the larger the displacement in the focus direction is, the larger the frictional force acts. Therefore, the relationship between the quasi-static displacement in the focus direction and the force has a hysteresis as shown in FIG. The fact that this quasi-static displacement has a large hysteresis is a problem because it is difficult to pull in when applying servo, and in the past, the surface accuracy of the bearing portion was increased as much as possible to deal with this. The present invention is an improvement over the above-mentioned drawbacks of the conventional device, and provides an objective lens driving device which reduces the hysteresis in the relationship between the quasi-static displacement in the focus direction and the force to facilitate the servo pull-in. The purpose is to An objective lens driving device according to the present invention includes a movable body supporting the objective lens, and a linear movement of the objective lens on the movable body in a focus direction and a tracking direction. A support mechanism that allows rotational movement, a coil holding portion that is made of a non-magnetic material and forms a part of the movable body, and a coil holding portion that is attached to the coil holding portion and is mounted at a position symmetrical with respect to the rotation axis of the movable body. A plurality of coils and a magnetic body, a permanent magnet and a yoke, and a magnetic circuit that forms a magnetic gap that gives a magnetic flux to each of the plurality of coils and the magnetic body. The body and the magnetic circuit
The movable body is opposed to the linear movement direction and the rotational movement direction through the magnetic gap, and at least a part of the magnetic body is arranged at a position where the magnetic flux from the magnetic gap is received and the magnetic body receives the magnetic field. It is configured to guide the movable body to a neutral position in the linear movement direction and the rotational movement direction by an attraction force, and both the magnetic circuit and the magnetic body forming the magnetic gap have curved surfaces on their opposing surfaces. It is characterized by being. The movable body and the magnetic circuit may be opposed to each other on a surface including a straight line parallel to the linear movement direction of the movable body. Further, the magnetic gap may have a substantially cylindrical shape. Further, the center positions of the coil and the magnetic body in the linear movement direction of the movable body can be made substantially coincident with each other. Further, the magnetic body may be arranged symmetrically with respect to an axis line of the rotational movement. According to the present invention having the above-described structure, the magnetic body is attached to the movable body supporting the objective lens, and the magnetic flux from the magnetic circuit acts to restore the movable body to the neutral position. Occurs. Further, since the yokes or the magnetic bodies that form the magnetic circuit have curved surfaces facing each other, the distance between the movable body and the magnetic circuit becomes constant in the movable range, and a stable attractive force always acts. FIG. 1 is a partial sectional perspective view showing an embodiment of the present invention, FIG. 2 (a) is a plan view thereof, and FIG. 2 (b) is a perspective view thereof.
Is a cross-sectional view thereof, and FIG. 3 is a perspective view showing a lens driving plate, a bobbin, and a positioning magnetic plate. The lens drive plate 5 has a bearing 7 which is free to rotate and slide around the shaft 6 in the central portion, and a coil bobbin 8 concentric with the bearing 7. The lens 9 and the counterweight 10 are attached to the lens driving plate 5 at positions facing each other with the shaft 6 interposed therebetween. A positioning magnetic plate 11 is joined to the portion of the bobbin 8 to which a magnetic field is applied so as to be axially symmetric with respect to the bearing 7, and a focusing coil 12 is wound around the positioning magnetic plate 11, and a tracking coil 13 (here, shown in the figure). (Omitted) is pasted. Then, a magnetic field is applied to a necessary portion by the magnet 14, the yoke 15 and the center pole 16 and an electric current is passed through the focusing coil 12, whereby the lens driving plate 5 and the lens 9
Moves in the direction of arrow B, and current is passed through the tracking coil 13, whereby the lens driving plate 5 rotates about the axis 6 and the lens 9 moves in the direction of arrow A. When the lens is displaced in the direction of arrow A, which is the tracking direction, a part of the positioning magnetic plate 11 is dislocated from the substantially cylindrical magnetic gap that gives a magnetic field to the coil, and the magnetic field energy in the space is increased. A restoring force is generated by the magnetic attraction force so that the energy is minimized. Even when the lens is displaced in the focus direction, the restoring force due to the magnetic attraction force can be similarly generated. Since the magnetic gap is formed in the focus direction and the tracking direction as described above, if a magnetic body is arranged at a position where the magnetic flux from the magnetic gap is received, the magnetic attraction force in the focus direction and the tracking direction. The restoration power is given by. Therefore, crosstalk between the focus direction and the tracking direction is reduced, and stable servo can be obtained. Further, since the positioning magnetic plate is arranged symmetrically with respect to the axis 1, no moment is generated around the axis A in the figure, so that the hysteresis is small in the relationship between the quasi-static static displacement and the force. The pull-in operation of is stable. Further, the structure using the positioning magnetic plate is simple and highly reliable. Further, as is apparent from FIG. 2, the yoke 15 forming the magnetic circuit and the positioning magnetic plate 11 have curved surfaces on the surfaces facing each other. For example, if both the yoke 15 and the positioning magnetic plate 11 have a rectangular shape or a convex portion, the flow of magnetic flux concentrates on that portion, and when the lens drive plate 5 moves in the magnetic circuit, magnetic attraction occurs. Movement becomes unstable due to disturbance of force. However, in the present invention, since the opposing surfaces of the positioning magnetic plate 11 and the yoke 15 are curved surfaces so that they are constant in the movable range, a stable attractive force always acts and the operation is stable. In the above embodiment, the case where the restoring force due to the magnetic force acts only in the tracking direction has been described.
Even if the width of the positioning magnetic plate in the focus direction is made equal to the width of the yoke in the focus direction as shown in FIG. 4, a restoring force in the focus direction can be provided. Here, as in the above-described embodiment, the coils 12, 13 and the positioning magnetic plate 11 are mounted so that their respective center positions in the longitudinal direction of the shaft 6 are substantially coincident with each other. As described above, according to the present invention,
Since the restoring force is given by the magnetic force, there is no crosstalk in the focus direction and the tracking direction, and stable servo can be obtained. Further, since the positioning magnetic plate is arranged symmetrically with respect to the bearing, the hysteresis is small in the relation between the quasi-static displacement and the force, and the servo pull-in operation is stable. Further, the structure using the positioning magnetic plate is simple and highly reliable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cross-sectional perspective view showing an embodiment of an objective lens driving device of the present invention. 2A and 2B are a plan view and a side sectional view of an objective lens driving device. FIG. 3 is a perspective view showing a lens driving plate, a bobbin, and a positioning magnetic plate used in the objective lens driving device. FIG. 4 is a side sectional view showing another embodiment of the present invention. FIG. 5 is a perspective view illustrating a conventional objective lens driving device. FIG. 6 is a plan view of a conventional objective lens driving device. FIG. 7 is a characteristic diagram showing the relationship between force and displacement in the focus direction in a conventional device. [Explanation of reference numerals] 1,6 ... Shafts 2, 8 ... Bobbins 3, 9 ... Lens 4 ... Damper 5 ... Lens drive plate 7 ... Bearing 10 ... Counterweight 11 ... Positioning magnetic plate 12 ... Focusing coil 13 ... Tracking coil 14 ... Magnet 15 ... Yoke 16 ... Center ball

Claims (1)

(57) [Claims] A movable body that supports the objective lens, a support mechanism that allows the movable body to move linearly in the focus direction and rotational movement in the tracking direction, and a part of the movable body that is made of a non-magnetic body A coil holder, a plurality of coils and a magnetic body attached to the coil holder, the plurality of coils and magnetic bodies being attached at positions symmetrical to the rotation axis of the movable body, and the plurality of coils and In an objective lens driving device having a magnetic circuit that forms a magnetic gap that gives a magnetic flux to each of the magnetic bodies, the movable body and the magnetic circuit are configured such that the magnetic body extends in the linear movement direction and the rotational movement direction of the movable body. The magnetic members are opposed to each other with a gap, and at least a part of the magnetic members is arranged at a position to receive the magnetic flux from the magnetic gap. While being configured to direct said movable member to a neutral position of said linear moving direction and the rotational moving direction by the magnetic attraction force received, both the magnetic circuit and the magnetic constituting the magnetic gap of the curved surface on the opposite surface An objective lens driving device characterized by being provided. 2. 2. The objective lens driving device according to claim 1, wherein the movable body and the magnetic circuit are opposed to each other with a surface including a straight line parallel to the linear movement direction of the movable body. 3. The objective lens driving device according to claim 1, wherein the magnetic gap has a substantially cylindrical shape. 4. The objective lens driving device according to claim 1, wherein the center positions of the coil and the magnetic body in the linear movement direction of the movable body are substantially coincident with each other. 5. 2. The objective lens driving device according to claim 1, wherein the magnetic body is arranged symmetrically with respect to an axis of the rotary movement.