Tilt correction method of movable portion, tilt correction method of objective lens for optical disk, and objective lens driving device for optical disk

In an objective lens driving device for an optical disk, a plurality of elastic supporting members supporting an objective lens have bent portions bent approximately in the focus direction and are arranged in parallel approximately in the focus direction to cause expansion/contraction of the elastic supporting members in the direction offsetting a moment M. With this structure, a tilt correction method of the movable portion, a tilt correction method of an objective lens for an optical disk, and an objective lens driving device for an optical disk can be provided capable of reducing the size of the movable portion, minimizing tilt of the objective lens in the focus direction to provide enhanced optical performance, and restraining a resonance peak by the elastic supporting members.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to tilt correction methods of a movable portion, tilt correction methods of an objective lens for an optical disk, and objective lens driving devices for an optical disk. More specifically, the present invention relates to a tilt correction method of a movable portion, tilt correction method of an objective lens for an optical disk, and an objective lens driving device for an optical disk for recording/reproducing information with respect to an optical disk of an optical information recording medium such as an MD, CD-ROM, and DVD.

2. Description of the Background Art

An optical recording/reproducing apparatus collects/scans as small spots of light beams over an information recording track of an optical disk for recording and erasing information. The optical recording/reproducing apparatus reads reflection of the light beam directed to an information recording surface for reproducing information.

When such an optical recording/reproducing apparatus records information, for example, the optical disk which is rotating at high speed may be subjected to surface vibration, decentering, and rotation oscillation. Accordingly, to reliably record, erase and reproduce information with respect to the optical disk, spots of light beams have to precisely follow the track even in the event of surface vibration or the like.

To meet this need, an objective lens for an optical disk used in an optical recording/reproducing apparatus is conventionally provided with a drive control mechanism which includes a focus servo mechanism adapted to slightly move in the perpendicular direction (optical axis direction) with respect to a disk surface, and a tracking servo mechanism adapted to slightly move in the radial direction with respect to the disk surface (orthogonal direction with respect to a recording track). The drive control mechanism has constantly provided positional control of an objective lens for an optical disk.

Now, a brief description of an objective lens driving device for an optical disk provided with a conventional drive control mechanism will be given with reference to the drawings.FIG. 42is a side view of an objective lens driving device for an optical disk101used for explaining a positional relationship between objective lens driving device for optical disk101and an optical disk10in the conventional art.FIG. 43shows an objective lens driving device for optical disk101when viewed from above.

As shown inFIGS. 42 and 43, objective lens driving device for optical disk101is positioned below optical disk10. The direction perpendicular to the surface of optical disk10(optical axis direction) is hereinafter defined as the focus direction Fo (the direction indicated by an arrow Fo in the drawing), the direction parallel to the surface of optical disk10and perpendicular to the track direction (radial direction of optical disk10) as the tracking direction Tr (the direction indicated by an arrow Tr in the drawing), and the tangential direction of the disk as the tangential direction Ta (the direction indicated by an arrow Ta in the drawing).

A reflection mirror9is provided on a base for guiding a laser beam to objective lens1. A movable portion includes: an objective lens1of a pickup optical system for an optical disk; an objective lens holder2for holding objective lens1approximately at the center; a pair of hollow focus coils6provided on the side walls of objective lens holder2; and a tracking coil7fixed at each focus coil6. The movable portion is supported by an elastic supporting member3of, for example, four parallel metal wires. Elastic supporting member3supports the movable portion in such a way to allow its slight movement in focus direction Fo and tracking direction Tr that are orthogonal to the longitudinal direction of elastic supporting member3.

Elastic supporting member3has one end mounted to a mounting member8fixed to the side surface of objective lens holder2that is orthogonal to tracking direction Tr, and the other end mounted to a fixed portion11(an optical base). Elastic supporting member3has, on its one or both surfaces (on both surfaces inFIG. 43), a damper material12. Note that mounting member8is used for mounting elastic supporting member3and serves to provide electrical communication among focus coil6, tracking coil7(these coils may be hereinafter collectively referred to as “a driving coil”), and metal elastic supporting member3.

Objective lens driving device for optical disk101is further provided with a magnetic circuit which includes a magnet4and a yoke5for driving objective lens holder2in focus direction Fo and tracking direction Tr. Yoke5consists of two inner yokes5(a) and two outer yokes5(b) which are orthogonal to the optical axis direction. Two magnets4are respectively mounted on the surfaces of two outer yokes5(b) that face inner yokes5(a).

Since inner yokes5(a) are inserted in focus coils6, objective lens holder2fixed to the driving coil can be driven by controlling a current flowing through the driving coil.

Namely, the magnetic circuit formed of magnet4and yoke5as well as focus coils6in the magnetic circuit comprise a dynamoelectric converter which causes movement in focus direction Fo. Thus, by controlling the current in focus coil6, the driving force in focus direction Fo can be varied. As a result, lens holder2mounted with objective lens1can be translated in focus direction Fo against the elastic force of elastic supporting member3.

Further, the magnetic circuit formed of magnet4and yoke5as well as tracking coil7positioned in the magnetic circuit comprise a dynamoelectric converter which causes movement in tracking direction Tr. Thus, by controlling the current in tracking coil7, the driving force in tracking direction Tr can be varied. As a result, lens holder2mounted with objective lens1can be translated in tracking direction Tr against the elastic force of elastic supporting member3.

Here, as a prior art elastic supporting member, an objective lens driving device disclosed in Japanese Patent Laying-Open No. 6-139599 (Japanese Patent No. 2981351) is illustrated.FIG. 44is a diagram an elastic supporting member (elastic material) of the objective lens driving device when viewed from above. Linear portions3aand3b, respectively extending from the movable and fixed portion sides of elastic supporting member3, are not collinear. Elastic supporting member3has a bent portion3cbetween linear portions3aand3b(elastic supporting member3is bent in tracking direction Tr).

A damper material12is fixed to connect an arm portion3dbranching from linear portion3aextending from the movable portion side and a protruding portion3e. Elastic supporting member3is in the form of a leaf spring with a damper material that has a damping effect applied on one or both surfaces.

The bent portion and damper material of the elastic supporting member serve to suppress vibration of the movable portion in focusing direction Fo and tracking direction Tr and suppress expansion/contraction or torsional oscillation in the longitudinal direction. Thus, a resonance peak is restrained to provide stable driving control.

However, the above described prior art objective lens driving device for the optical disk suffers from the following problems.

The above described prior art objective lens driving device for optical disk tends to deform (expand/contract) in the longitudinal direction because of the bent portion of elastic supporting member3. For example, as shown in schematic side views ofFIGS. 45A,45B, and45C, when objective lens1is vertically moved in focus direction Fo, it tilts in a specific direction. Namely, the optical axis (solid lines in the drawings) of objective lens1are inclined.

FIG. 45Bshows that the movable portion is in a neutral position and the optical axis is not inclined.FIG. 45Ashows that objective lens1is moved upwardly in focus direction Fo.FIG. 45Cshows that objective lens is moved downwardly in focus direction Fo. As shown inFIG. 45A, when objective lens1is moved upwardly in focus direction Fo, the optical axis is inclined toward fixed portion11(+side) in the Ta direction (tangential direction) in the drawing. As shown inFIG. 45C, when objective lens1is moved downwardly in focus direction Fo, the optical axis is inclined toward the side opposite fixed portion11(−side) in the Ta direction (tangential direction) in the drawing.

If objective lens1is inclined as described above, deflection of elastic supporting member3produces a moment on the movable portion. For example, if the supporting interval of four parallel elastic supporting members3(having a length of 11.45 mm) is 8.26 mm in width and 2.91 mm in height and objective lens1is vertically moved by 0.4 mm in focus direction Fo, when elastic supporting member3has a bent portion, a tilt amount would be about ±7.6′ in the Ta direction. On the other hand, if the elastic supporting member has an linear shape without any bent portion (in this case deformation is unlikely to occur in the longitudinal direction), the tilt is caused by deformation of elastic supporting member3, and hence the tilt would be no more than about ±0.4′ in the Ta direction.

Further, the tilt is affected by the supporting interval of elastic supporting member3.FIG. 46is a graph showing a relationship between the interval of the elastic supporting members in the height direction and a tilt amount of the optical axis of the objective lens when only the interval in the height direction is varied in the case of the above described elastic supporting member3. It also represents the tilt amount of the optical axis when objective lens1is moved upwardly in focus direction Fo by 0.4 mm. As can be seem fromFIG. 46, the smaller the interval between the elastic supporting members in the height direction is, the greater the tilt amount of the objective lens optical axis is. As the movable portion is reduced in size and thickness, the interval of the elastic supporting members in the height direction decreases and the tilt amount of the objective lens optical axis increases, whereby the problem becomes more serious.

In recent years, the amount of information that an optical recording/reproducing apparatus is required to process is rapidly increased. It is desired that a recording surface density for optical recording is considerably increased accordingly. The recording surface density can be increased for example by reducing the wavelength of a light source or by providing an objective lens with greater numerical aperture. As to the former method of reducing the wavelength of the light source in the optical recording/reproducing apparatus, although light sources having a wavelength of about 780 nm or 650 nm are primarily used, the usage of light sources is gradually shifting to those of violet or blue having a wavelength of about 400 nm.

To mention the effect of coma aberration, since coma aberration is in inverse proportion to the wavelength of a light source, it increases with reduction in the wavelength of the light source. Accordingly, to reduce coma aberration, a tilt amount on the side of the optical recording/reproducing apparatus must be reduced to about 50–60% of the current amount. With the increasing need for reducing the tilt amount in the optical recording/reproducing apparatus, the tilt amount allowed to an actuator is desirably 50% or lower of the current amount. For example, if the tilt amount of optical axis of the objective lens when the objective lens is vertically moved in focus direction Fo is currently allowed to have about ±7.6′ in the Ta direction (with light source wavelength of 780 nm), in the case of a optical recording/reproducing apparatus with a light source wavelength of 410 nm, a tilt amount must be restrained to about ±4′.

SUMMARY OF THE INVENTION

Therefore, the present invention is made to solve the aforementioned problems. An object of the present invention is to provide a tilt correction method of a movable portion, a tilt correction method of an objective lens for an optical disk, and an objective lens driving device for an optical disk for correcting a tilt caused when a movable portion is moved, providing accurate recording and reproducing properties even if the movable portion is reduced in size, restraining a resonance peak by suppressing torsional oscillation of an elastic supporting member for signals in focusing and tracking directions, and providing stable driving control of the objective lens driving device.

In the tilt correction method of the movable portion according to the present invention, the movable portion and a fixed portion are connected by a plurality of elastic supporting members, the movable portion is displaceably provided in the direction orthogonal to the longitudinal direction of the elastic supporting member (hereinafter referred to as the orthogonal direction), and a tilt of the movable portion caused when the movable portion is moved in the orthogonal direction is corrected. By varying expansion/contraction amounts of the plurality of elastic supporting members when the movable portion is moved in the orthogonal direction, the tilt of the movable portion is corrected.

In the above mentioned invention, preferably, each of the plurality of elastic supporting members has at least one bent portion. By varying expansion/contraction amounts of the bent portions of respective elastic supporting members when the movable portion is moved, the tilt of the movable portion is corrected.

According to the tilt correction method of the movable portion of the present invention, unlike the conventional case where a tilt of a movable portion is caused by a moment produced on the movable portion due to deflection of the elastic supporting member when the movable portion is moved in the orthogonal direction, the provision of the bent portion in the orthogonal direction of the movable portion provides expansion/contraction of the elastic supporting member in the direction against the moment, i.e., the direction offsetting the moment, whereby the tilt of the movable portion can be minimized.

According to the tilt correction method of an objective lens for an optical disk of the present invention, a movable portion holding an objective lens, a fixed portion, and a plurality of elastic supporting members connecting the movable portion and fixed portion and elastically supporting the movable portion in a manner displaceable at least in the focus direction are provided. A tilt of the movable portion caused with movement in the focus direction is corrected. The elastic supporting member has at least one bent portion which is bent approximately in the focus direction. The bent portions of the elastic supporting members positioned in parallel in the focus direction are adjusted to provide expansion/contraction of the elastic supporting members in the direction offsetting a moment caused by the deflection of the elastic supporting member.

According to the tilt correction method of the objective lens for the optical disk, a tilt caused in the focus direction of the objective lens due to the moment produced on the movable portion caused by the deflection of the elastic supporting member as a result of movement in the focus direction of the optical axis of the objective lens can be minimized by expansion/contraction of the elastic supporting members caused in the direction against the moment, i.e., the offsetting direction, by the bent portions extending approximately in the focus direction and toward neighboring elastic supporting members.

The objective lens driving device for an optical disk of the present invention is provided with a movable portion holding an objective lens, a fixed portion, and a plurality of elastic supporting members connecting the movable portion and fixed portion and elastically supporting the movable portion in a manner displaceable at least in the focus direction. The device is provided with a correction controlling unit for correcting a tilt of the movable portion caused when the movable portion is moved in the focus direction by adjusting deflections of elastic supporting members arranged in parallel in the focus direction to cause expansion/contraction of the elastic supporting members in the direction offsetting moments caused by the deflections of the elastic supporting members.

With this objective lens driving device for optical disk, although a tilt of the objective lens is caused in the focus direction due to a moment of the movable portion produced by the deflection of the elastic supporting member, by adjusting deflections of neighboring elastic supporting members provided approximately in the focus direction to cause expansion/contraction of the elastic supporting members in the direction against the moment, i.e., in the offsetting direction, the tilt of the objective lens can be minimized in the focus direction.

As the movable portion is reduced in thickness, i.e., the interval between the elastic supporting members arranged in parallel in the focus direction decreases, the tilt of the objective lens in the focus direction increases. However, the tilt of the objective lens can be corrected as described above and the interval between the elastic supporting members can be reduced. As a result, the device can be reduced in thickness and size.

In the above described invention, preferably, the elastic supporting member has at least one bent portion approximately in the focus direction for adjustment of deflection.

With this structure, although a tilt is caused to the movable portion due to a moment produced on the movable portion caused by deflection of the elastic supporting member when the movable portion is moved approximately in the focus direction, the bent portion which is bent approximately in the focus direction of the movable portion causes expansion/contraction of the elastic supporting member in the direction against the moment, i.e., offsetting direction, whereby the tilt of the movable portion can be minimized.

In the above described invention, two elastic supporting members arranged in parallel approximately in the focus direction are symmetric about a surface perpendicular to the focus direction.

In the above described invention, preferably, two elastic supporting members arranged in parallel approximately in the focus direction have an inclined portion.

With this structure, expansion/contraction of the elastic supporting member at the bent portion and expansion/contraction of the elastic supporting member at the inclined portion are caused in the opposite directions, considerable expansion/contraction of the elastic supporting member at the bent portion can be offset by the inclined portion. Thus, the bent portion is allowed to have a sufficient bending length, thereby facilitating provision of a damper material which suppresses vibration of the elastic supporting member. As a result, a resonance peak can be restrained.

In the above described invention, preferably, two elastic supporting members arranged in parallel approximately in the focus direction have a bent portion which is bent approximately in the tracking direction.

With this structure, a sufficient damping effect is obtained at the bent portion which is bent in the tracking direction. Further, the tilt of the optical axis the objective lens can be corrected at the bent portion which is bent in the focus direction, whereby an effect similar to the above mentioned effect can be obtained.

In the above described invention, preferably, two elastic supporting members arranged in parallel approximately in the focus direction both have bent portions generally in a shape of a square with one side opened.

With this structure, although expansions/contractions are caused in opposite directions, since two elastic supporting members both have a bent portion generally in a shape of a square with one side opened, a greater amount of expansion/contraction is caused at the bent portion in the position where a deflection angle of the elastic supporting member is greater. Thus, the tilt of the objective lens in the focus direction can be corrected and a bending length can be set to produce a sufficient damping effect. Further, the device can be reduced in thickness by reduction of intervals between the elastic supporting members as described above.

In the above described invention, preferably, the elastic supporting members arranged in parallel approximately in the focus direction are provided with the above mentioned bent portions at the same position from the fixed portion, where the bent portion has a different bending length.

In the above described invention, preferably, the elastic supporting members arranged in parallel approximately in the focus direction are provided with the above-mentioned bent portions at different positions from the fixed portion, where the bent portion has the same bending length.

With this structure, the elastic supporting members arranged in parallel approximately in the focus direction have bent portions bending in the same direction with differing bending lengths. The greater bending length provides greater amount of expansion/contraction. Thus, when the objective lens is moved in the focus direction, the elastic supporting member on the side opposite the disk contracts by a greater amount when the objective lens is moved toward the disk in the focus direction, and the elastic supporting member positioned on the disk side contracts by a greater amount when the objective lens is moved toward the side opposite the disk in the focus direction.

As a result, expansion/contraction of the elastic supporting member is caused in the direction against the moment caused by deflection of the elastic supporting member, i.e., the offsetting direction, so that the tilt of the objective lens optical axis can be minimized as described above, and the movable portion can be reduced in thickness in size, facilitating provision of a damping material which suppresses vibration of the elastic supporting member. Thus, a resonance peak can be restrained.

By varying bending positions of the bent portions which are bent in the same direction of the elastic supporting members arranged in parallel in the optical axis direction, the bent portion at a position with a greater deflection angle is subjected to a greater amount of expansion/contraction. Thus, when the objective lens is moved in the focus direction, the elastic supporting member positioned on the side opposite the disk contracts by a greater amount when the objective lens is moved toward the disk in the focus direction, and the elastic supporting member positioned on the disk side contracts by a greater amount when the objective lens is moved toward the side opposite the disk in the focus direction.

As a result, expansion/contraction of the elastic supporting member is caused in the direction opposite the moment, i.e., the offsetting direction, whereby the tilt of the optical axis of the objective lens can be minimized as described above, and the movable portion can be reduced in thickness and size, facilitating provision of a damper material which suppresses vibration of the elastic supporting member. Thus, a resonance peak can be restrained.

In the above described invention; preferably, the elastic supporting member is provided in such a way that a straight line connecting the fixing positions on the movable portion and fixed portion sides is approximately in parallel with the disk surface.

With the above described structure, the elastic supporting members positioned in parallel in the optical axis direction are asymmetric about a surface perpendicular to the focus direction. Thus, although a certain amount of tilt of the objective lens optical axis may be inevitably caused when the objective lens is moved in the tracking direction, such tilt can be minimized by setting a straight line connecting the fixing positions on the movable portion and fixed portion sides to be approximately in parallel with the disk surface.

In the above described invention, preferably, an arm portion and a protruding portion of free ends of the elastic supporting member are connected through a damper material near the above mentioned at least one bent portion of the elastic supporting member.

In the above described invention, preferably, the movable portion is supported in a manner displaceable approximately in the radial direction, where the displacement in the radial direction is rotation approximately about a center of gravity.

With the above described structure, a tilt correction effect can be produced as described above during focus movement. In addition, since movement in the tracking direction is made by rotation, when movements in the tracking and focus directions are simultaneously made, positional displacement does not occur between a power point of focus movement and a center of gravity. Thus, the objective lens may not tilt due to a moment caused by positional displacement of the power point and center of gravity. Consequently, the tilt of the objective lens can be minimized during movements are simultaneously made in the focus and tracking directions, not to mention during focus and radial movements.

More preferably, the elastic supporting member is provided as inwardly inclined from the fixed portion side toward the movable portion side.

With the above described structure, when an empty weight is applied in the tracking direction, the effect of an empty weight drop of the objective lens can be minimized because of a considerable empty weight drop of the bent portion. Thus, when used for a portable device, a current consumption for positioning the lens can be minimized, so that a power consumption can also be minimized.

With the above described structure, a simple structure formed solely of the elastic supporting member can suppress vibration in the focusing and tracking directions and torsional oscillation of the elastic supporting member, so that a resonance peak can be restrained.

In the optical recording/reproducing apparatus of the present invention, the objective lens driving device for the optical disk is used as a device for recording, reproducing and erasing optical information.

In the above described invention, preferably, the optical recording/reproducing apparatus records, reproduces, and erases optical information with use of a light source of a short wavelength of violet or blue.

With the above described structure, the tilt in the focusing direction can be minimized during movement of the objective lens, so that light spots are favorably and accurately recorded and reproduced with respect to the disk. Even when the light source of a short wavelength of about 400 nm is used, light spots can be favorably and accurately recorded and reproduced with respect to the disk and vibration of the elastic supporting member can be suppressed. As a result, a more stable servo property is obtained. In addition, the overall size of the apparatus can be reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First of all, the concept of the present invention will be described with reference to the drawings and mathematical expressions.

FIGS. 1 and 2show that a movable portion13is supported by elastic supporting members3and fixed portion11. InFIG. 1, movable portion13is supported by two parallel elastic supporting members3.FIG. 2shows that movable portion13is displaced by δ in the y direction.

Referring toFIGS. 1 and 2, a moment M is produced around each elastic supporting member3. As a result, movable part13is inclined by α. Here, a moment produced on movable portion13will be considered. First of all, the x axis is defined in parallel with elastic supporting member3in the direction orthogonal to the longitudinal direction of elastic supporting member3, the y axis is defined perpendicular to the x axis, and the length of elastic supporting member3is defined as L. Further, the moment, deflection angle and deflection amount when movable portion13is displaced by δ are calculated.

Note that E is Young's modulus, F is shear force, M is moment, I is cross sectional secondary moment of elastic supporting member, i is deflection angle, y is deflection amount, and C1–C4 are constants.

Based on the balance relationship, the following equations can be derived.

If a boundary condition is x=0, then y=0 and dy/dx=0. If x=L, then y=δ and dy/dx=0. Thus, shear force F, moment M, deflection angle i and deflection amount y are expressed as follows.
F=12EIδ/L3
M=6EIδ(2x−L)/L3
i=6δx(L−x)/L3
y=δx2(3L−2x)/L3(5)

As shown inFIG. 2, at the position where x=L, i.e., at the position where elastic supporting member3is fixed to movable portion13, moment M (6EIδ/L12) of elastic supporting member3is applied clockwise to movable portion13, whereby movable portion13is inclined as shown by a chain-dotted line in the drawing.

Here, the concept of the present invention is that inclination by angle δ by moment M of movable portion13is offset by changing the length of each elastic supporting member3in the x direction, i.e., by changing the expansion/contraction amount of each elastic supporting member3in the x direction.

By way of example,FIG. 3shows elastic supporting member3provided with a bent portion in the y axis direction. Moment M is offset by varying length of the bent portion of elastic supporting member3in the x direction. Namely, with the bending length of p, if a displacement amount of elastic supporting member3is δ, the length of the bent portion in the x direction at upper elastic supporting member3would be greater by a=p·sin(i). The length of the bent portion at lower elastic supporting member3in the x direction is smaller by a=p·sin(i). Here, deflection angles i refer to deflection angles at the position where x=b. By thus varying the lengths of elastic supporting members3during movement of movable portion13, moment M applied to movable portion13is offset and tilt of movable portion13can be corrected. Based on the above described concept of the present invention, the embodiments of an objective lens driving device for an optical disk will be described in detail.

First Embodiment

Referring toFIG. 4, the structure of objective lens driving device for optical disk100will be described. Note thatFIG. 4is a side view schematically showing an objective lens driving device for optical disk100according to a first embodiment of the present invention. An optical disk10is shown for clarifying a positional relationship of the device with respect to the optical disk.

Overall Structure of Objective Lens Driving device for Optical Disk100

Objective lens driving device for optical disk100includes: an objective lens1of a pickup optical system for an optical disk; a reflection mirror3for directing a laser beam to objective lens1; an objective lens holder2for holding objective lens1approximately at the center; a pair of hollow focus coils (not shown, having the same structure as the conventional case) provided on side walls of objective lens holder2; a tracking coils7fixed to respective focus coils; and an elastic supporting member3of four parallel metal wires supporting objective lens holder2. Elastic supporting member3supports the movable portion including objective lens holder2in a manner slightly displaceable in the focus direction Fo and tracking direction Tr orthogonal to the longitudinal direction of elastic supporting member3.

Further provided are: a mounting member8mounting one end of elastic supporting member3to objective lens holder2and the other end to fixed portion11and supplying a current to a driving coil (formed of the focus coil and tracking coil7); and a magnetic circuit formed of a magnet4and yoke5for driving objective lens holder2in focus direction Fo and tracking direction Tr. Objective lens driving device for optical disk100is provided such that objective lens1is positioned below a prescribed track of optical disk10.

The overall structure and driving concept of objective lens driving device for optical disk100are similar to those of the prior art, and therefore detailed description of the overlapping portion will not given here.

Structure of Elastic Supporting Member3

Now, the structure of elastic supporting member3, which is a key portion of the present embodiment, will be described in detail.FIG. 5is a side view of objective lens driving device for optical disk100showing elastic supporting member3.FIG. 5shows movable portion13formed of objective lens1, objective lens holder2, driving coil (not shown) and the like, fixed portion11, and elastic supporting member3connecting movable portion13and fixed portion11.

Elastic supporting member3has a bent portion3cthat makes a linear portion3aextending from movable portion13and a linear portion3bextending from fixed portion11placed on different straight lines. Bent portion3cextends approximately in the optical axis14direction from fixed portion11and extends in the direction toward neighboring elastic supporting member3.

FIG. 6is an elevational perspective view of elastic supporting member3. One example thereof is shown inFIG. 3. Elastic supporting members3fixed to fixed portion11are on both sides of movable portion13to surround a center of gravity of movable portion13. Elastic supporting members3arranged in parallel in the optical axis14direction (focus direction Fo) are symmetric about a surface perpendicular to the focus direction. It is also desirable that elastic supporting members3arranged in parallel in tracking direction Tr are symmetric about a surface perpendicular to the focus direction.

Deflection of Elastic Supporting Member3

Here, deflection amount of elastic supporting member3when objective lens of movable portion13is displaced in focus direction Fo will be described.FIG. 7shows in a side view deflection of elastic supporting member3when elastic supporting member3is a linear beam supported at both ends. In the drawing, elastic supporting member3(having a length of 11.45 mm) in a linear shape without a bent portion has one end fixed to fixed portion11and the other end fixed to movable portion13.FIG. 7Arelates to the case where no deformation occurs, andFIG. 7Brelates to the case where deformation of elastic supporting member3occurs when the objective lens (movable portion13) is moved by 0.4 mm toward the disk side (upward) in focus direction Fo. The deflection angle of elastic supporting member3is determined depending on the position of elastic supporting member3in the longitudinal direction.

FIG. 8shows a relationship between the longitudinal position (mm) and deflection angle (rad) of a beam (elastic supporting member). A point of 0 in the longitudinal direction of the beam corresponds to the end of elastic supporting member3on the movable portion side. A point 11.45 mm in the beam's longitudinal direction correspond to the end of elastic supporting member3on the fixed portion side. As shown inFIG. 8, when elastic supporting member3is deflexed, deflection angles at both ends of elastic supporting member3become 0 and the intermediate point of elastic supporting member3attains to a maximum angle.

FIG. 9shows in a side view deflection of elastic supporting member3when the objective lens (driving member) of elastic supporting member3having a bent portion of the present embodiment is moved in focus direction Fo. The length of 11.45 mm of elastic supporting member3includes lengths of linear portions3aand3bexcluding bent portion3c.FIG. 9Arelates to the case where deformation does not occur.FIG. 9Brelates to the case where deformation of elastic supporting member3occurs when the objective lens (movable portion13) is moved by 0.4 mm toward the side of the disk (upward) in focus direction Fo. Linear portions3aand3bare subjected to deflection of about the same deflection amount and deflection angle as in the case ofFIGS. 7 and 8.

Here, if the deflection angle at the position of bent portion3cin the longitudinal direction of elastic supporting member3is θ, bent portion3cofFIG. 9is also inclined by θ. Thus, the inclination of θ of bent portion3cincreases the length of elastic supporting member3in the longitudinal direction by L, as compared withFIG. 9A.

FIG. 10shows in a side view deflection of elastic supporting member3and movement of the movable portion when linear elastic supporting member3free from any bent portion, as shown inFIG. 7, is used.FIG. 10shows that four parallel linear elastic supporting members3have one ends fixed to fixed portion11and the other ends fixed to movable portion13. Elastic supporting member3arranged in parallel with the focus direction Fo is fixed with supporting interval L1.

In this state, deformation of elastic supporting member3and inclination of optical axis14are shown when objective lens1(movable portion13) is moved by a distance L toward the disk (upward) in focus direction Fo. When each elastic supporting member3is deflexed as shown by a thick line ofFIG. 10, a moment M is applied in the arrow direction (clockwise) to movable portion13, and optical axis14tilts by θ2toward fixed portion11in tangential direction Ta with respect to a straight line perpendicular to the disk. The magnitude of θ2is affected by L1and L2, material of elastic supporting member3(Young's modulus), amount of expansion/contraction in the longitudinal direction and so on.

FIG. 11shows in a side view deflection of elastic supporting member3and movement of movable portion11when elastic supporting member3having a bent portion of the present embodiment as shown inFIG. 9is used.FIG. 11shows four parallel elastic supporting members3each having linear portions3a,3band bent portion3c. Here, bent portion3cis bent approximately in the optical axis direction and toward neighboring elastic supporting members3as shown by a thick line. Each elastic supporting member3has one end fixed to fixed portion11and the other end fixed to movable portion13. The interval of elastic supporting members3arranged in focus direction Fo is fixed to L1. In this state, deformation of elastic supporting member3and tilt of optical axis13when objective lens1(movable portion13) is moved toward the disk (upward) by distance L2in focus direction Fo are shown.

Function

If deflection angles of upper and lower elastic supporting members3in the drawing at the position of bent portions3cin the longitudinal direction of elastic supporting member3are respectively θ3and θ4, when each elastic supporting member3is deflexed as shown by a thick line ofFIG. 11, the bent portions of upper and lower elastic supporting members3are respectively inclined by θ3and θ4.

Thus, as compared with the case where deflection occurs when no bent portion is provided, the length of upper elastic supporting member3increases in the longitudinal direction by L3, whereas lower elastic supporting member3decreases in length in the longitudinal direction by L4. Thus, elastic supporting member3expands/contracts to cause tilt in the direction opposite moment M indicated by an arrow ofFIG. 10, i.e., toward the side opposite fixed portion11in tangential direction Ta. As a result, elastic supporting member3acts to offset tilt θ2ofFIG. 10, whereby the tilt of movable portion13in tangential direction Ta can be minimized.

For example, each of four elastic supporting members3having bent portions3cas shown inFIG. 11is formed of a material of beryllium copper, having a total length of 11.45 mm and a bent portion of a bending length of 0–0.56 mm at the position 9.76 mm from the end on the side of the movable portion. In addition, supporting intervals on the movable portion side in focus direction Fo and tracking direction Tr are respectively set to 2.51 mm and 8.26 mm. Then, tilt of the optical axis in tangential direction Ta when the objective lens is moved by 0.4 mm toward the side of the disk (upward) in focus direction Fo was calculated by analysis. The resultant relationship between “length of bending portion” and “tilt” is shown inFIG. 12. Note that (−) and (+) of tilt values respectively represent tilts of optical axis toward the side opposite fixed portion11and toward the side of fixed portion11in tangential direction Ta.

As can be seen fromFIG. 12, by varying the lengths of bent portions, the tilt of the optical axis can be controlled. The greater the bending portion length is, the greater the tilt amount toward (−) side is. This is because elastic supporting member3expands/contracts to cause tilt in the direction opposite moment M as indicated by an arrow inFIG. 10, i.e., toward the side opposite fixed portion11in tangential direction Ta. Referring toFIG. 12, the provision of a small bending portion having a length of about 0.01 mm can serve to restrain tilt to 0′. However, the length of the bending portion must be set depending on the material, shape, length, supporting interval, position of the bending portion and the like of elastic supporting member3. In addition to the length of the bent portion, the position of the bent portion may be changed to control tilt.

FIG. 13shows the analysis result of a relationship between “position of bent portion” and “tilt.” This analysis model is obtained with the length of the bent portion set to 0.56 mm as in the above described model ofFIG. 12. As previously stated with reference toFIG. 8, since the deflection angle varies according to the position of the bent portion, the closer the bent portion is to the central portion of elastic supporting member3in the longitudinal direction, the expansion/contraction function of elastic supporting member3in the longitudinal direction becomes considerable. Thus, expansion/contraction of elastic supporting member3is caused to the direction opposite moment M indicated by an arrow ofFIG. 10, i.e., toward the side opposite fixed portion11in tangential direction Ta. As a result, a tilt amount toward the side of (−) becomes large. Referring toFIG. 13, by setting bent portion1at the position around 11.4 mm, tilt can be restrained to 0′. However, the position of the bent portion can be set to enable control depending on the material, shape, length, supporting interval, length of bent portion and the like of elastic supporting member3.

Effect

As described above, conventionally, tilt of optical axis14of objective lens1varies according to moment M applied to movable portion13due to deflection of elastic supporting member3during movement of movable portion13in focus direction Fo. However, the provision of the bent portion bending approximately in the optical axis direction and toward neighboring elastic supporting member3in movable portion13causes expansion/contraction of elastic supporting member3in the direction opposite moment M, i.e., in the offsetting direction, whereby the tilt of optical axis14of objective lens1can be minimized.

Further, as the movable portion is reduced in thickness, i.e., as the interval between elastic supporting members3arranged in parallel in the optical axis direction, tilt of optical axis14of objective lens1becomes greater. However, the tilt of objective lens1can be corrected to enable reduction in thickness and size of a device.

First Modification

Structure

FIG. 14is a side view showing a first modification of elastic supporting member3of the above described objective lens driving device for optical disk100.FIG. 15shows a side view of another example according to the first modification. As shown inFIGS. 14 and 15, the distance between upper and lower elastic supporting members3arranged in parallel in the direction of optical axis14form a slop portion that increases in the direction of optical axis14from fixed portion11toward movable portion13. L1near portions3band3acorrespond to the slope portion respectively inFIGS. 14 and 15.

Here, the function of elastic supporting member3(thick solid line) ofFIG. 15when objective lens1is moved toward the disk (upward) in focus direction Fo will be described with reference to the side view ofFIG. 16.

FIG. 16Ashows only a portion of elastic supporting member3ofFIG. 15including linear portions3band bent portion3cextending from fixed portion11.FIG. 16Bshows a portion of elastic supporting member3ofFIG. 15that includes only linear portion3a.

Function and Effect

As shown inFIG. 16A, the bent portion is inclined along a linear deflection angle. Thus, upper elastic supporting member3inFIG. 16Aextends in the longitudinal direction and lower elastic supporting member in the drawing contracts in the longitudinal direction, whereby a straight line connecting leading edges of the bent portions are inclined in the direction indicated by an arrow ofFIG. 16A(counterclockwise).

As shown inFIG. 16B, if the upper and lower elastic supporting members3are provided to have a slope portion that increases in the direction of optical axis14from fixed portion11toward movable portion13, upper and lower elastic supporting members3in the drawing respectively expands and contracts in the longitudinal direction, whereby a straight line connecting the leading edges of linear portion3ais inclined in the direction indicated by an arrow inFIG. 16B(clockwise).

By setting bent portion3csuch that the tilt of the bent portion (FIG. 16A) is greater than that of the slope portion (FIG. 16B), expansion/contraction of elastic supporting member3is caused in the direction opposite moment M (FIG. 10), i.e., in the offsetting direction, during movement in focus direction Fo. As a result, the tilt of optical axis14of objective lens1can be minimized.

Further, the tilt shown inFIG. 16Bcan offset the tilt shown inFIG. 16A, so that bent portion3cis allowed to have a greater length. Accordingly, the length of bent portion3cbecomes sufficiently large, thereby facilitating provision of a damper member that suppresses vibration of elastic supporting member3. As a result, a resonance peak can be restrained.

In addition, the above mentioned function and effect can be produced in the case of a structure in which linear portion3bhas a slope portion as shown inFIG. 14. By setting bent portion3csuch that the tilt of the bent portion is greater than that of the slope portion, expansion/contraction of elastic supporting member3is caused in the direction opposite moment M, i.e., in the offsetting direction, during movement in focus direction Fo. As a result, the tilt of optical axis14of objective lens1can be minimized. Further, the tilt of bent portion3ccan be offset by the tilt of the slop portion, so that bent portion3cis allowed to have a greater length. Accordingly, the length of bent portion3cbecomes sufficiently large, thereby facilitating provision of a damper member that suppresses vibration of elastic supporting member3. As a result, a resonance peak can be restrained.

In the case where both of linear portions3aand3bof elastic supporting member3have a slope portion, by providing bent portion3csuch that tilt of bent portion3cis greater than a total tilt amount of linear portions3aand3bhaving the slope portion, the above described effect can be produced.

Second Modification

Structure

FIG. 17shows a second modification of elastic supporting member3in objective lens driving device for optical disk100. As shown inFIG. 17, elastic supporting member3additionally has a bent portion bending approximately in tracking direction Tr, so as to produce an effect similar to that of the above described objective lens driving device for optical disk100.FIG. 17Ais a side view and17B is a plan view when seen from the disk side.

As shown inFIGS. 17A and 17B, each elastic supporting member3has linear portions3a,3b, bent portion3cbending approximately in the direction of optical axis14and toward neighboring elastic supporting members3, and a bent portion3fbending approximately in tracking direction Tr. In this configuration, bent portion3cis provided such that bent portion3foffsets greater tilt in the direction of moment M (tilt toward fixed portion11in tangential direction Ta) by tilt (tilt in the direction opposite fixed portion11in tangential direction Ta) of bent portion3c.

Function and Effect

Thus, expansion/contraction of elastic supporting member3is caused in the direction opposite moment M, i.e., in the offsetting direction, during movement of movable portion10in focus direction Fo, whereby tilt of optical axis14of the objective lens can be minimized. Further, bent portion3fmay have a sufficiently large length, thereby facilitating provision of a damper material that suppresses vibration of elastic supporting member3. Thus, a resonance peak can be restrained.

The above described elastic supporting member3shown inFIG. 17can be manufactured by forming a structure having linear portions3aand3band bent portion3fwhich is bent in tracking direction Tr by means of etching or the like, and then bending linear portion3ato form bent portion3cwhich is bent from fixed portion11approximately in the direction of optical axis14and toward neighboring elastic supporting member3.

Alternatively, elastic supporting member3may be manufactured by forming a structure having linear portions3a,3band bent portion3cby etching or the like and then bending linear portion3bto provide bent portion3fwhich is bent in tracking direction Tr.

Third Modification

Structure

FIG. 18shows a third modification of elastic supporting member3in objective lens driving device for optical disk100. Another example of the third modification is shown inFIG. 19. As shown inFIGS. 18 and 19, elastic supporting member3includes linear portions3a,3band bent portion3cwhich is bent from fixed portion11approximately in the direction of optical axis14and toward neighboring elastic supporting member3. It further has a second bent portion3gwhich is bent from fixed portion11approximately in the direction of optical axis14and toward neighboring elastic supporting member3at the position where a deflection angle (a deflection angle when objective lens1is moved) of elastic supporting member3is smaller than that of a bent portion3c.

Function and Effect

Elastic supporting member3having the above described structure can minimize tilt of optical axis14of objective lens1as in the case of the previously described each elastic supporting member3. Here, the graph ofFIG. 20shows a relationship between the position in the longitudinal direction and a deflection angle of the linear beam shown inFIG. 8.FIGS. 20A and 20Brespectively relate to upper elastic supporting members3ofFIGS. 18 and 19, showing a relationship between bent portions3c,3gof each elastic supporting member3and a deflection angle.

FIGS. 20A and 20Brespectively relates to bent portions3cand3g. It can be seem that the bending position of bent portion3cis at the position where a deflection angle is greater than that of bent portion3g. In this configuration, expansions/contractions are caused in the opposite directions since bent portions3cand3gare bent in the opposite directions from fixed portion11. As a result, bending portion3cthat is positioned at the portion where the deflection angle of elastic supporting member3is greater produces a greater effect of expansion/contraction. Thus, upper and lower elastic supporting members3act in the same manner, so that the tilt of optical axis14of objective lens1can be corrected. In addition, since tilt of bent portion3ccan be offset by that of bent portion3g, the bending length that is enough to produce a sufficient damping effect can be ensured. Further, the distance between elastic supporting members3can be further reduced as in the above described case, thereby enabling reduction in thickness of the device.

Fourth Modification

Structure

FIG. 21shows a fourth modification of elastic supporting member3in the objective lens driving device for optical disk. At least one pair of elastic supporting members3are arranged in parallel in the direction of optical axis14of objective lens1. Elastic supporting member3has a bent portion3hbending approximately in the direction of optical axis14from fixed portion11toward the side opposite neighboring elastic supporting member3. Elastic supporting members3positioned in parallel in the direction of optical axis14are symmetric about a surface perpendicular to the focus direction. The distance between elastic supporting members3decreases from the fixed portion side toward the movable portion side in the direction of optical axis14, forming linear portion3awith a slope.

Function and Effect

As in the above described each elastic supporting member3, elastic supporting member3of the fourth modification can minimize tilt of optical axis14of objective lens1.

In this configuration, bent portion3his provided such that tilt of linear portion3ahaving a slope is greater than that of bent portion3h. Thus, expansion/contraction of elastic supporting member3is caused in the direction opposite moment M, i.e., in the offsetting direction, during movement of movable portion13in focus direction Fo, whereby tilt of optical axis14of the objective lens can be minimized. Further, since the tilt of bent portion3hcan be offset by that of linear portion3a, bent portion3his allowed to have a sufficiently large length. As a result, provision of a damper material that suppresses vibration of elastic supporting member3is facilitated and a resonance peak can be restrained.

Note that the above described function and effect are not limited to the case where linear portion3aof elastic supporting member3has a slope. The similar effect can be produced when linear portion3bhas a slope portion or both of linear portions3aand3bhave slope portions if bent portion3hand the slope portions are adjusted such that tilt of linear portion3awith the slope is greater than that of bent portion3h.

Fifth Modification

Structure

FIG. 22shows a fifth modification of elastic supporting member3in objective lens driving device for optical disk100. As shown inFIG. 22, at least one pair of elastic supporting member3are arranged in parallel in the direction of optical axis14of objective lens1, each elastic supporting member3positioned in the direction of optical axis14has a bent portion3iwhich is bent from fixed portion11approximately in the direction of optical axis14and in the direction toward the optical disk. Bent portion3iof elastic supporting member3that is closer to the disk (elastic supporting member3on the upper side of the drawing) is shorter in length.

Function and Effect

Elastic supporting member3having the above described configuration can minimize tilt of optical axis14of objective lens1as in the case of the above described elastic supporting member3. Bent portion3iof lower elastic supporting member3that is bent in the same direction from fixed portion11is made longer. For example, when objective lens1is moved toward the disk (upward) in focus direction Fo, lower elastic supporting member3contracts to a large extent in the longitudinal direction. As a result, expansion/contraction of elastic supporting member3is caused in the direction opposite moment M due to deflection of elastic supporting member3, i.e., in the offsetting direction. Thus, tilt of optical axis14of objective lens1can be minimized.

To give details ofFIG. 22, for example, each elastic supporting member3is formed of a beryllium copper. Elastic supporting member3has a total length of 11.45 mm. Bent portion3iis positioned 9.76 mm from the end on the side of movable portion13, and the longer bending portion has a fixed length of 0.56 mm. The supporting interval on the side of movable portion13in focus direction Fo is 2.91 mm and that in tracking direction Tr is 8.26 mm.

FIG. 23shows a result obtained by analysis with this structure for optical axis tilt in tangential direction Ta when objective lens1is moved toward the disk (to the upper side) by 0.4 mm in focus direction Fo. InFIG. 23, the abscissa represents “length of shorter bent portion” and the ordinate represents “tilt” of optical axis14in tangential direction Ta (tilt values of (+) and (−) respectively represent tilt toward fixed portion11and toward the side opposite the fixed portion). As can be seen fromFIG. 23, in the above described configuration, the shorter bending length is set to 0.36 mm, so that tilt in tangential direction Ta can be restrained approximately to 0′.

In addition, the distance between elastic supporting members3can be reduced to enable reduction in thickness and size of movable portion13. A bending length that is required for providing a damper material that suppresses vibration of elastic supporting member can be ensured for upper and lower elastic supporting member3, whereby a resonance peak can be restrained.

Structure

FIG. 24shows another example of the above described fifth modification. As shown inFIG. 24, at least one pair of elastic supporting members3are arranged in parallel in the direction of optical axis14of objective lens1. Each elastic supporting member3has a bent portion3jwhich is bent approximately in the direction of optical axis14from fixed portion11and in the direction opposite the disk side. Bent portion3jof elastic member3positioned closer to the disk (an elastic supporting member positioned on the upper side of the drawing) has a greater length.

Function and Effect

Similarly to elastic supporting member3shown inFIG. 22, elastic supporting member3having the above described structure can minimize tilt of optical axis14of objective lens1. Bent portion3jof upper elastic supporting member3that is bent in the same direction (in the direction opposite the disk) from fixed portion11is made longer. For example, when objective lens1is moved toward the disk (upward) in focus direction Fo, upper elastic supporting member3contracts to a large extent in the longitudinal direction. As a result, expansion/contraction of elastic supporting member3is caused in the direction opposite moment M due to deflection of elastic supporting member3, i.e., in the offsetting direction. Thus, tilt of optical axis14of objective lens1can be minimized.

Further, since a distance between elastic supporting members3can be reduced, reduction in thickness and size of the movable portion is enabled. In addition, a bending length required for providing a damper material that suppresses vibration of elastic supporting member3can be ensured for upper and lower elastic supporting members3, so that a resonance peak can be restrained.

Sixth Modification

Structure

FIG. 25shows a sixth modification of elastic supporting member3in the objective lens driving device for optical disk. At least one pair of elastic supporting members3are arranged in parallel in the direction of optical axis14of objective lens1. Elastic supporting member3has a bent portion3iwhich is bent approximately in the direction of optical axis14from fixed portion11and in the direction toward the optical disk. Bent portion3iof elastic supporting member3that is closer to the disk is arranged in a position where the deflection angle of elastic supporting member3is smaller.

As shown inFIG. 26of another example of the sixth modification, at least one pair of elastic supporting members3are arranged in parallel in the direction of optical axis14of objective lens1. Elastic supporting member3has a bent portion3jthat is bent in the direction of optical axis14from fixed portion11and in the direction opposite the disk. Bent portion3jof elastic supporting member3farther from the disk is arranged in a position where the deflection angle of elastic supporting member3is smaller.

Function and Effect

As in the case of each respective supporting member3, elastic supporting member3showing the above described structure ofFIGS. 25 and 26can minimize tilt of optical axis14of objective lens1.

For example, a graph ofFIG. 27shows a relationship between “longitudinal position” and “deflection angle” at the bent portion of the linear beam shown inFIG. 8.FIGS. 27A and 27Brespectively relates to upper and lower elastic supporting members3shown inFIG. 26. A relationship between the bent portion and deflection angle of each elastic supporting member3is shown. As can be seen inFIG. 27, upper bent portion3jofFIG. 27Ais arranged in a position with a greater deflection angle than lower bent portion3jofFIG. 27B. With this structure, upper elastic supporting member3is displaced to a greater extent in the longitudinal direction of elastic supporting member3than lower elastic supporting member3. Namely, upper elastic supporting member3becomes longer in the longitudinal direction, so that expansion/contraction of elastic supporting member3is caused in the direction opposite moment M due to deflection of elastic supporting member3, i.e., in the offsetting direction. As a result, tilt of optical axis14of the objective lens can be minimized. In addition, a bending length which is sufficient to produce a damping effect can be ensured, a resonance peak is restrained and the distance between elastic supporting members3can be reduced. Thus, the device can be reduced in thickness.

Seventh Modification

Structure

A seventh modification of the objective lens driving device for optical disk is shown. Preferably, as shown inFIGS. 28,29and30, a straight line connecting fixing positions on the sides of movable portion13and fixed portion11is set approximately in parallel with the disk surface.

Function and Effect

With this structure, the optical axis tilt (tilt toward the direction of Tr) when objective lens1is moved in tracking direction Tr can be minimized. Because of asymmetry of elastic supporting members3arranged in parallel in the direction of optical axis14about a surface perpendicular to the focus direction, when a straight line connecting fixing positions on the sides of movable portion13and fixed portion11is not parallel to the disk surface, movement of the objective lens in tracking direction Tr may cause imbalance of elastic supporting members3arranged in the tracking direction, whereby tilt may be caused in tracking direction Tr.

More specifically, each elastic supporting member3inFIG. 28is formed of a beryllium copper. Each elastic supporting member3has a total length of 11.45 mm. The bent portion is provided in a position 9.76 mm from the end of the movable portion. The longer and shorter bending lengths are respectively 0.56 mm and 0.36 mm. The supporting interval of the movable portions arranged in focus direction Fo is 2.91 mm, and that in tracking direction Tr is 8.26 mm. With this structure, a result of the optical axis tilt in the tangential direction obtained by analysis is 0′ when objective lens1is moved by 0.4 mm toward the disk side (upper side) in focus direction Fo.

Here,FIG. 31shows a result of the optical axis tilt in tracking direction Tr obtained by analysis when objective lens1is moved by 0.2 mm toward the lower side of the sheet of the drawing with the configuration of the above described elastic supporting member3.

InFIG. 31, the mark ♦ (difference in height of fixed portions) shows that a straight line connecting fixing positions of movable portion13and fixed portion11is not parallel to the disk surface (there are height differences of 0.36 mm and 0.56 mm respectively on the upper and lower sides) (for example the structure of elastic supporting member3shown inFIG. 22). The mark Δ (heights of fixed portions are the same) shows that a straight line connecting fixing positions on the sides of movable portion13and fixed portion11is approximately in parallel with the disk surface.

As can be seen fromFIG. 31, by making a straight line connecting fixing positions on the sides of movable portion13and fixed portion11approximately in parallel with the disk surface, if the shorter bending portion has a length of 0.36 mm such that the optical axis tilt in tangential direction Ta is 0′ when the objective lens is moved by 0.4 mm toward the disk (upper side) in focus direction Fo, the optical axis tilt in tracking direction Tr can be restrained to about 0′ when the objective lens is moved by 0.2 mm in the forward direction orthogonal to the sheet of the drawing in tracking direction Tr.

Thus, since neighboring elastic supporting members3arranged in parallel in the direction of optical axis14are asymmetric about a surface perpendicular to the focus direction, the optical axis tilt of objective lens1may be caused when objective lens1is moved in the tracking direction. However, such tilt of optical axis14of the objective lens can be minimized by setting the straight line connecting fixing positions on the sides of movable portion13and fixed portion11approximately in parallel with the disk surface.

The above discussion relates to elastic supporting member3shown inFIG. 28. Even in the case of elastic supporting members3respectively shown inFIGS. 29 and 30, a similar function and effect can be produced.

Second Embodiment

Now, referring toFIG. 32, an objective lens driving device according to a second embodiment of the present invention will be described.FIG. 32is a view showing the objective lens driving device of the second embodiment when viewed from above. The device includes: a movable portion13including an objective lens1, an objective lens holder, a focus coil6, a tracking coil7, a mounting member8and the like; fixed portion11; and an elastic supporting member3connecting movable portion13and fixed portion11. Elastic supporting member3is provided to be inwardly inclined from fixed portion11toward movable portion13. The above described elastic supporting member3of the present invention can be applied to such a structure. With this structure, in addition to a tilt correction effect as described above, the following effect can be obtained during focus movement.

First of all, movement in the tracking direction will be described in detail.FIG. 33shows a prior art example where four beams are mounted in parallel. InFIG. 33, G and F respectively represent a center of gravity and a power point on the focus side.FIG. 33Arelates to the case where the objective lens is in a neutral position not moved in the tracking direction.FIG. 33Brelates to the case where the objective lens is moved in the tracking direction (in the left direction indicated by an arrow). As shown inFIG. 33A, when a force is applied in the focus direction in the neutral position, the movable portion is displaced approximately in the focus direction since center of gravity G and focus power point F are on the same straight line. However, if a force is applied in the focus direction with the objective lens displaced in the tracking direction (the left direction indicated by an arrow) as shown inFIG. 33B, the central position of a magnetic circuit, i.e., power point F and center of gravity G of the movable portion would not be placed on the same straight line. A moment is produced in the arrow direction as shown at the bottom ofFIG. 33B, thereby causing optical axis displacement in the tracking direction.

Now, movement in the tracking direction of the structure shown inFIG. 32will be described. InFIG. 34, G and F respectively represent a center of gravity and power point in the focus direction.FIG. 34Arelates to the case where the objective lens is in a neutral position not moved in the tracking direction.FIG. 34Brelates to the case where the objective lens is moved in the tracking direction (in the left direction indicated by an arrow). As shown inFIG. 34A, when a force is applied in the focus direction in the neutral position, the movable portion is displaced approximately in the focus direction since center of gravity G and focus power point F are on the same straight line. As shown inFIG. 34B, if a force is applied in the focus direction with the objective lens moved in the radial direction (the left direction indicated by an arrow), rotation in the tracking direction is caused. Thus, the central position of the magnetic circuit, i.e., power point F and center of gravity G of the movable portion are placed on the same straight line. Accordingly, in the structure ofFIG. 34, unlike the structure which causes parallel tracking movement as inFIG. 33, tilt is caused to the objective lens due to a moment caused as a result of displacement of power point F and center of gravity G. Namely, the optical axis would not tilt.

Based on the above, an experiment was conducted by analysis with use of a supporting beam shown inFIG. 35. Each supporting member has a total length of 8.0 mm. The length from the fixed portion to a bent portion is 3 mm, a distance of the bent portion is 0.2 mm, and the bending length is 0.3 mm. The supporting members are vertically symmetric in the focus direction. The upper and lower beams are in parallel with an interval of 3 mm.

The beam has a thickness of 0.05 mm and a width of 0.06 mm. The width of the bent portion is 0.12 mm. Although not shown, the supporting member is provided inwardly from the fixed portion side toward the movable portion side at an angle of 90°.

With this structure, tilt of the optical axis was measured with the objective lens moved vertically by 0.4 mm from the central point in the focus direction and horizontally moved by 0.2 mm from the central position in the tracking direction. Then, the measured tilt was approximately 0 and, even if the objective lens was moved both in the focus direction and radial direction, the optical axis tilt was approximately 0.

Further, a shift amount (self weight drop) when a gravitational force is applied in the tracking direction will be described.FIG. 36shows beams each having a bent portion in the tracking direction.FIG. 36Ashows a structure in which the bent portion is bent outwardly from the fixed portion side toward the movable portion side.FIG. 36Bshows a structure in which the bent portion is bent inwardly from the fixed portion side toward the movable portion side. When a gravitational force is applied in the direction indicated by an outline arrow to a beam supported at both ends, in the case ofFIG. 36A, the objective lens tends to shift not only in the same direction as the gravitational force but also in the direction opposite the direction of the gravitational force because of the bent portion. InFIG. 36B, the objective lens is shifted in the same direction as the gravitational force direction, and the shift amount of the objective lens tends to increase in the gravitational force direction because of the bent portion.

For example, the supporting member ofFIG. 36has a total length of 8.9 mm. The length from the fixed portion side to the bent portion is 4 mm, and the bending length is 0.3 mm. The upper and lower beams are arranged in parallel with an interval of 3 mm to be vertically symmetric in the focus direction. The beam has a thickness of 0.05 mm and a width of 0.06 mm. The width of the bent portion is 0.12 mm. The beam is provided inwardly from the fixed portion side toward the movable portion side at an angle of 90°. In this structure, an amount of displacement from the center of the objective lens when a gravitational force is applied to the movable portion of about 280 mg in the tracking direction was measured by analysis. In the case ofFIG. 36A, a shift amount was 4.9 μm in the direction opposite the gravitational force direction. In the case ofFIG. 36B, a shift amount was 7.7 μm in the same direction as the gravitational force. On the other hand, an amount of displacement from the center of the objective lens when a gravitational force is applied to the movable portion of about 280 mg in the tracking direction was 1.2 μm in the same direction as the gravitational force, in the case ofFIG. 35. It can be seen that the shift amount of the objective lens is smaller than in the case ofFIG. 36.

In the structure where the bending portion is provided in the tracking direction, the shift amount of the objective lens when the gravitational force is applied in the tracking direction increases because of the bent portion. However, if the bent portion which is bent in the focus direction is provided as in the present invention, shift due to the gravitational force can be restrained.

Function and Effect

With the above described structure, when the objective lens is shifted in the focus and radial directions not to mention during focus and radial movements, the tilt of the objective lens can be minimized. In addition, when used for a portable device where gravitational forces are applied in all directions, less power is used for aligning the lens center. Thus, power consumption can be minimized.

Third Embodiment

Structure

Now, referring toFIGS. 37 and 38, an elastic supporting member3of an objective lens driving device according to the third embodiment of the present invention will be described. As shown inFIGS. 37 and 38, elastic supporting member3of the present embodiment includes an arm portion3dof a free end branching from elastic supporting member3around at least one bent portion (3cofFIG. 37,3iofFIG. 38), a protruding portion3eformed at a connecting portion with respect to fixed portion11, where at least arm portion3dand protruding portion3eare connected by a damper material12.

Function and Effect

With elastic supporting member3of the third embodiment, the bent portion (3cofFIG. 37,3iofFIG. 38) of each elastic supporting member3, which is bent approximately in the direction of optical axis14, serves to minimize tilt of optical axis14of the objective lens, as stated previously. Further, simple configuration of elastic supporting member3suppresses vibrations in focusing direction Fo and tracking direction Tr as well as torsional oscillation of elastic supporting member3. Thus, a resonance peak can be restrained.

Fourth Embodiment

Structure

Now, referring toFIG. 39, elastic supporting member3of an objective lens driving device of the fourth embodiment of the present invention will be described. As shown inFIG. 39, a pair of elastic supporting members3arranged in the direction of optical axis14of objective lens1are integrally formed and separated after assembly.FIG. 39shows that elastic supporting member3can be formed by etching a thin plate of a beryllium copper. Two elastic supporting members3arranged in parallel in focus direction Fo are connected by a portion3k, which is disconnected after assembly.

Function and Effect

With elastic supporting member3of the fourth embodiment, elastic supporting members3arranged in parallel in the direction of optical axis14are integrally formed to enable facilitate assembly. As compared with the case where two elastic supporting members3arranged in parallel in the focus direction are positioned for example with use of a jig for assembly, elastic supporting members3are integrally formed, so that a bending position, a tilt angle of the slope portion, vertical arrangement and the like can be more precisely determined. Thus, tilt correction of the optical axis can be more accurately performed.

Fifth Embodiment

Structure

Now, referring toFIG. 40, an optical recording/reproducing apparatus200of the fifth embodiment of the present invention will be described.FIG. 40is a top view schematically showing optical recording/reproducing apparatus200provided with objective lens driving device for optical disk100of the first embodiment.

Referring toFIG. 40, optical recording/reproducing apparatus200includes a spindle motor16for rotating optical disk10, objective lens driving device for optical disk17, an optical unit19provided with a laser unit or an optical part18, including various types of lenses and prisms, and a feeding mechanism20enabling movement of optical unit19.

In the above described optical recording/reproducing apparatus200, feeding mechanism20enables movement of optical unit19and slight movement of the movable portion of objective lens driving device for optical disk100at high speed. Thus, spots of laser beams can follow a prescribed track of optical disk10which is rotating at high speed.

Although objective lens driving device for optical disk100of the first embodiment is used as an objective lens driving device for optical disk here, any other device may be used.

FIG. 41shows an analysis result pertaining to transfer properties of a servo system in objective lens driving device for optical disk100(using elastic supporting member3shown inFIG. 5). An arrow indicated by Fo corresponds to transfer properties of a focus system, and an arrow indicated by Tr corresponds to transfer properties of a tracking system. The ordinate and abscissa respectively represents vibration (dB) and frequency (Hz) in logarithmic representation.

As can be seen fromFIG. 41, no resonance is found between frequencies of 100 Hz and 20 kHz after a primary resonant point, exhibiting favorable transfer properties. The above described other shapes of elastic supporting members3also exhibited favorable properties.

Function and Effect

As described above, in the optical recording/reproducing apparatus using the objective lens driving device for optical disk, tilt of optical axis14is minimized during movement of the objective lens. Thus, spots are precisely directed to the disk to allow favorable and accurate recording/reproduction. Since vibration of elastic supporting member3can be restrained, a more stable servo property is obtained. In addition, the movable portion can be reduced in thickness, so that the overall thickness of the device can be reduced.

In the optical recording/reproducing apparatus, if a light source of a short wavelength of about 400 nm is used, coma aberration increases with reduction in wavelength since it is in inverse relationship with the wavelength. For example, coma aberration differs by about 1.9 times between wavelengths of 780 nm and 410 nm. To reduce coma aberration, the tilt amount on the side of the optical recording/reproducing apparatus must be reduced by about 50%. Thus, it is desirable that the tilt amount allowed to the actuator is about 50% or lower of the current value.

As described above, in the conventional objective lens driving device for optical disk shown inFIGS. 42 and 43, if the current acceptable amount (wavelength of 780 nm) of tilt is ±7.6′ when the objective lens is vertically moved in the focus direction (±0.4 mm), the tilt must be restrained to about ±4′ in the device using a light source having a wavelength of 410 nm. However, the use of elastic supporting member3of the present embodiment can restrain tilt to about 0′, offsetting the acceptable tilt amount of the other parts.

With use of elastic supporting member3of the present embodiment, the tilt of optical axis14can be minimized during movement of the objective lens. Thus, spots are precisely directed to the disk to enable accurate recording/reproduction. Even if a light source with a short wavelength of about 400 nm is used, spots are precisely directed to the disk for accurate recording/reproduction and vibration of elastic supporting member3can be suppressed. As a result, a more stable servo property can be obtained. In addition, the overall thickness of the device can be reduced.

In the above, the shape, size and material of elastic supporting member3are exemplified. However, such a shape, size and material are not limited to those specified above and the structure of the objective lens driving device is not limited to that specified above.

In each of the above described embodiments, a tilt correction method of a movable portion which is a distinguishing feature of the present invention is applied to the tilt correction method for the objective lens of optical disk and the objective lens driving device for optical disk. However, the present invention is not limited to the tilt correction method of the objective lens for optical disk and the objective lens driving device for optical disk. The present invention can also be applied to a device in which a movable portion and fixed portion are connected by a plurality of elastic supporting members and the movable portion is provided in a manner displaceable in the direction orthogonal to the longitudinal direction of the elastic supporting member (hereinafter referred to as the orthogonal direction) and which requires correction of tilt of the movable portion caused when the movable portion is moved in the orthogonal direction.

According to the tilt correction method for movable portion, tilt correction method for objective lens of optical disk, and objective lens driving device for optical disk of the present invention, by adjusting deflections of neighboring elastic supporting members approximately arranged in the focus direction, expansion/contraction of the elastic supporting members is caused in the direction opposite the moment, i.e., in the offsetting direction, whereby tilt of the objective lens in the focus direction can be minimized. In addition, the tilt of the objective lens can be corrected and the distance between the elastic supporting members can be reduced. As a result, the device can be reduced in thickness and size.