Optical element retaining device, optical element transfer device and optical pickup device

An element holding device of the present invention includes: a guide portion engaging with a guide shaft; a lens fixing portion on which to fix a collimator lens; an arm portion; an insertion portion having a hole portion in which to insert a guide shaft; a wire fixing portion made by protruding a side surface of the insertion portion in a −Y direction; and a wire fixed on the wire fixing portion. A bent portion being a leading end portion of the wire is housed in a slit. Thereby, excess deformation of a contact portion is suppressed.

This application claims priority from Japanese Patent Application Number JP 2011-215924 and JP 2011-177353, the content of which are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical element holding device configured to hold an optical element such as a collimator lens, an optical element moving device, and an optical pickup apparatus.

2. Description of the Related Art

A common optical pickup apparatus reads/writes information from/to an optical disc by irradiating an information recording layer of the optical disc with a laser beam and receiving the laser beam reflected by the information recording layer, i.e., returning light.

A spherical aberration occurs according to the thickness of a cover layer covering an information recording layer, depending on the standard of an optical disc. Further, different spherical aberrations occur even in one optical disc of a certain standard if the disc has multiple information recording layers, because the position of an information recording layer relative to a cover layer varies depending on which information recording layer is subjected to read/write operations.

An objective lens for CD/DVD has a function of correcting spherical aberration by diffractive annular zones provided in a surface of the lens. However, since an optical disc of the BD standard, for example, employs an objective lens of high NA, it is difficult to correct spherical aberration caused by the objective lens.

To cope with this, such spherical aberration is corrected by moving a collimator lens placed in the midway of the optical path of a laser beam, by a predetermined amount. This feature will be described with reference toFIGS. 10A to 10C.FIGS. 10A and 10Beach show a device while cutting away a portion of the device, in which the cut portion is hatched.

A conventional optical element moving device100will be described with reference toFIG. 10A, where X directions indicate directions parallel with a laser beam passing through a collimator lens, Y directions indicate directions orthogonal to the X directions on a plane where guide shafts102and103are placed, and Z directions indicate directions orthogonal to the X directions and the Y directions.

The optical element moving device100shown inFIG. 10Amainly includes: an element holding portion101configured to hold a collimator lens104; the guide shaft103engaging with a +Y direction-side end portion of the element holding portion101; the guide shaft102inserted in a hole portion located in a −Y direction-side end portion of the element holding portion101; and a screw-shaped feed shaft105configured to move the element holding portion101by a predetermined amount.

The feed shaft105is a screw-shaped member having a thread groove in its periphery, and a nut107made of a resin material is screwed to the feed shaft105. In addition, plate-shaped nut holding portions108and109are placed at the −Y direction-side end portion of the element holding portion101. The nut holding portions108and109are configured to sandwich the nut107from both sides in the X directions with the feed shaft105inserted therein.

When the feed shaft105is rotated by a drive force of a stepping motor106with the above configuration, the nut107is moved in conjunction with the rotation. Then, the nut107presses any one of the nut holding portions108and109to move the element holding portion101in the X directions by a predetermined amount.

There is a slight play between the feed shaft105and the nut107. In this state, the nut107is not fixed to the feed shaft105and thus backlash occurs therebetween. Due to this backlash, the position of the collimator lens104held by the element holding portion101might not be fixed. To solve this, a spring110configured to press the element holding portion101in the +X direction is inserted on the guide shaft102at a position on a −X side of the element holding portion101. This allows the nut holding portion108to press the nut107in the +X direction, which removes the play between the feed shaft105and the nut107, suppresses the above-described backlash, and thereby fixes the position of the collimator lens104.

However, the optical element moving device100of the above configuration might cause a failure due to the employment of the nut107. Specifically, when the nut107is made to strike against a −X direction-side or +X direction-side end portion to move the element holding portion101back to its initial position, the nut107sometimes bites the thread groove of the feed shaft105at the end portion and cannot escape therefrom. In addition, the feed shaft105is set slightly longer than the movable range of the element holding portion101to have enough length to get the element holding portion101back to its initial position. With this configuration, the stepping motor106keeps applying a driving force to the feed shaft105for a while even after the element holding portion101is moved to an origin detection position if the element holding portion101is placed near the initial position. In this case, the nut107keeps pressing the nut holding portions108and109while this drive force is applied, which makes the nut107bite the feed shaft105.

Further, as shown inFIG. 10B, an upper portion of the nut107is covered with a nut holding portion111. Hence, as shown inFIG. 10C, the nut107keeps hitting the nut holding portion111while the stepping motor106is in normal operation, which results in noise and vibration.

Furthermore, the employment of the nut107requires multiple parts such as the nut holding portions108and109and the spring110, which complicates assembly work.

A structure using a spring instead of the above nut is disclosed in Japanese Patent Application Publication No. 2010-165445 (Patent Document 1). Referring to FIGS. 7 and 8 of Patent Document 1, the torsion coil spring 80 is attached to the lens holder 62, and a side surface of the torsion coil spring 80 at a position near its leading end portion engages with the groove of the feed screw 63. This configuration enables a mechanism of moving the collimator lens 61 without a nut, and thus avoids the problems caused by the nut.

However, with the invention described in Patent Document 1, the mounting of the torsion coil spring to the optical pickup apparatus is sometimes not easy. Specifically, referring to FIGS. 11A and 11B and their description of Patent Document 1, the torsion coil spring 80 has one end being in contact with the feed screw 63 and the other end fixed by a second press-fix portion 72. Hence, when attached to the optical pickup apparatus, the lens holder 62 needs to be incorporated in the housing of the optical pickup apparatus with such shape of the torsion coil spring 80 kept. This work is very complicated and might reduce work efficiency.

The present invention has been made in view of such circumstances. An objective of the present invention is to provide an optical element holding device in which a spring is in contact with a feed shaft with a simple configuration, an optical element moving device, and an optical pickup apparatus.

SUMMARY OF THE INVENTION

An optical element holding device of the present invention configured to hold a lens in such a way that the lens is movable along a guide shaft, comprises: an insertion portion having a hole portion in which to insert the guide shaft; an element fixing portion formed integrally with the insertion portion and on which to fix the lens; the lens placed in the element fixing portion; a fixing portion placed on a side different from a side where the element fixing portion is placed and protruding to the outside from the insertion portion; and a wire having a helically-wound wound portion fitted on the fixing portion and having a part placed outside a leading end of the fixing portion, wherein a part of the wire is housed in a housing area provided in a leading end portion of the fixing portion.

An optical element moving device of the present invention comprises: a feed shaft placed along an optical path of a laser beam, having a helical thread groove in a surface thereof, and configured to be rotated by a drive force of a motor; a guide shaft placed substantially parallel with the feed shaft; and the optical element holding device described above, wherein a side surface of the part of the wire, which protrudes outside the fixing portion of the optical element holding device, is in contact with the thread groove of the feed shaft.

An optical pickup apparatus of the present invention comprises: a light-emitting element configured to emit a laser beam; an objective lens configured to focus the laser beam on an information recording layer of an optical disc; a light-receiving element configured to receive returning light which is the laser beam reflected by the information recording layer; and the optical element moving device according to claim6configured to move a collimator lens being the lens along an optical path of the laser beam.

An optical element moving device of the present invention comprises: a feed shaft placed along an optical path of a laser beam, having a helical thread groove in a surface thereof, and configured to be rotated by a drive force of a motor; a guide shaft placed substantially parallel with the feed shaft; an optical element holding portion placed to be movable along the guide shaft while a lens is fixed thereon and the guide shaft is inserted therein or engages therewith; and a spring fixed on the optical element holding portion, formed by winding a wire around an axis directed toward the feed shaft, and having a side surface of the wire in contact with the thread groove of the feed shaft.

An optical pickup apparatus of the present invention comprises: a light-emitting element configured to emit a laser beam; an objective lens configured to focus the laser beam on an information recording layer of an optical disc; a light-receiving element configured to receive returning light which is the laser beam reflected by the information recording layer; and the optical element moving device described above configured to move a collimator lens being the lens along an optical path of the laser beam.

An optical element moving device of the present invention configured to hold a lens configured to move along a laser beam, comprises: an element fixing portion on which to fix the lens; an insertion portion formed integrally with the fixing portion and in which to insert a guide shaft; a fixing portion protruding from a side surface of the insertion portion to the outside; and a spring inserted on the fixing portion, formed by winding a wire around an axis directed perpendicular to the side surface of the insertion portion, and placed in such a way that at least a part of the spring protrudes outside an end portion of the fixing portion.

DESCRIPTION OF THE INVENTIONS

An element holding device50, an optical element moving device11, and an optical pickup apparatus10according to an embodiment of the present invention will be described with reference toFIGS. 1 to 7.

In this embodiment, the optical pickup apparatus10is configured to read/write information.FIG. 1shows the configuration of the optical pickup apparatus10. The optical element moving device11is incorporated in the optical pickup apparatus10and configured to move an optical element such as a collimator lens.FIGS. 3A and 3Bshow the configuration of the optical element moving device11. The element holding device50is incorporated in the optical element moving device11and configured to hold the optical element such as a collimator lens in such a way that the element is movable.FIGS. 4A and 4Bshow the configuration of the element holding device50.

Referring toFIG. 1, the optical pickup apparatus10has a configuration compatible with optical discs of the CD (Compact Disc) standard, the DVD (Digital Versatile Disc) standard, and the BD (Blu-ray Disc) standard, for example.

The general function of the optical pickup apparatus10is to read/write information from/to an optical disc by irradiating an information recording layer of the optical disc with a laser beam and receiving the laser beam having been reflected by the information recording layer. In this respect, the optical disc from/to which information is read/written may have a single information recording layer or, alternatively, have multiple (two or more) information recording layers.

Meanwhile, a blue-violet (blue) laser beam with a wavelength range of 395 nm to 420 nm (with a wavelength of 405 nm, for example) is used in the BD standard, a red laser beam with a wavelength range of 645 nm to 675 nm (with a wavelength of 650 nm, for example) is used in the DVD standard, and an infrared laser beam with a wavelength range of 765 nm to 805 nm (with a wavelength of 780 nm, for example) is used in the CD standard.

In the following description, X directions indicate directions parallel with the optical path of a laser beam passing through a collimator lens22, Y directions indicate directions orthogonal to the X directions on a plane where guide shafts46and48are placed, and Z directions indicate directions orthogonal to the X directions and the Y directions. In addition, a principal surface of a housing12, where a concave portion in which elements constituting the optical pickup apparatus are incorporated can be observed, is referred to as a back surface, and a surface opposed to the back surface is referred to as a front surface.

The optical pickup apparatus10of this embodiment is formed by placing various elements at their predetermined positions of the housing12made by integral resin molding. In this respect, the elements to be housed in the optical pickup apparatus include electronic components and optical elements through which a laser beam passes or on which a laser beam is reflected. For example, inFIG. 2, examples of the electronic components include laser devices38and39and PDICs36and37, and examples of the optical elements include semitransparent mirrors30and32, AS plates34and35, and the collimator lens22.

The housing12is made by injection molding of a resin material, such as PPS (Poly Phenylene Sulfide Resin), or the like. The housing12includes a substantially plate-shaped bottom surface portion15and a sidewall portion13made by protruding an edge portion of the bottom surface portion15in a thickness direction of the housing12. Moreover, guide holes14in which to insert a guide shaft are provided at a +X direction-side edge portion of the housing12, whereas a guide groove16with which a guide shaft engages is provided at a −X direction-side edge portion of the housing12. As a material of the housing12, die-casting alloy made mainly of aluminum (Al), magnesium (Mg), or zinc (Zn) may be used instead.

Although not illustrated, an inner sidewall portion is also provided inside the optical pickup apparatus10to protrude in the Z directions from the bottom surface portion15. Components constituting the optical pickup apparatus10are fixedly attached to the sidewall portion13or the inner sidewall portion.

Shown in the drawings are only components constituting the element holding device50and the optical element moving device11which are the gist of this embodiment. Specifically, the guide shafts46and48, the collimator lens22, the element holding device50, a wire52, a feed shaft44, and a stepping motor54are housed in the housing12. Further, various elements to be described later with reference toFIG. 2are also housed in an area surrounded by the sidewall portion13. Although not illustrated, a holder configured to hold an objective lens is placed on a surface opposed to the bottom surface portion15in such a way as to be movable by an actuator.

The optical elements included in the optical pickup apparatus10will be described with reference toFIG. 2. The optical pickup apparatus10includes a first optical system40for forming an optical path of a laser beam of the BD standard and a second optical system42for forming an optical path of laser beams of the DVD standard and the CD standard. Note that the optical pickup apparatus10does not necessarily have to have the two optical systems, but may have one optical system shared by these three standards. When the one optical system is shared by these three standards, the collimator lens22is adjusted to an optimal position according to these standards.

The first optical system40of the BD standard includes the laser device38, a diffraction grating31, the semitransparent mirror30, the collimator lens22, a reflecting mirror20, an objective lens28, the AS plate34, and the PDIC36.

The laser device38is made by packaging light-emitting elements configured to emit a laser beam with which to irradiate a disc26of the BD standard. In this respect, the laser device38may be made as a so-called CAN-type package or, alternatively, made as a lead frame-type package.

The diffraction grating31is configured to split a laser beam having been emitted by the laser device38into a zero-order diffracted light beam, a positive first-order diffracted light beam, and a negative first-order diffracted light beam.

The semitransparent mirror30is configured to reflect a laser beam having been emitted by the laser device38and passed through the diffraction grating31as well as to transmit a laser beam having been reflected by the disc26(returning light).

The collimator lens22is configured to convert a laser beam having been reflected by the semitransparent mirror30into a parallel light beam. In addition, the collimator lens22can be displaced along an optical axis, and is configured to correct spherical aberration caused by a cover layer covering an information recording layer of the disc26. The collimator lens22is moved while being incorporated in the optical element moving device11to be described later with reference toFIGS. 3A and 3B.

The reflecting mirror20is configured to receive a laser beam having been transmitted through the collimator lens22, and to reflect the received laser beam so that the laser beam can proceed at right angle to the information recording layer of the disc26.

The objective lens28is placed right above the reflecting mirror20, and is configured to focus a laser beam having been reflected by the reflecting mirror20on a signal recording layer of the disc26.

The AS plate34is configured to give aberration for servomechanism to a laser beam having been reflected by the disc26and passed through the optical elements. As will be described later, the AS plate34is not an essential component, but there is also a model without the AS plate34.

The PDIC36is a photodiode integrated circuit element for signal detection and functions as a photodetector. The PDIC36is configured to generate a light-reception output containing an information signal component as well as a servo signal component used for focus servo and tracking servo, upon reception of a laser beam for BD.

The read/write operations of the first optical system40are performed as follows.

First, a laser beam having been emitted by the laser device38passes through the diffraction grating31to be split into a zero-order diffracted light beam, a positive first-order diffracted light beam, and a negative first-order diffracted light beam. Such split is carried out to allow the PDIC36to obtain a servo signal used for focus servo and tracking servo. Then, the laser beam having been thus split is reflected by the semitransparent mirror30, is then converted into a parallel light beam by the collimator lens22, and is then reflected by the reflecting mirror20to proceed toward the disc26in a direction perpendicular thereto. Thereafter, the laser beam is focused on the signal recording layer of the disc26by refraction and diffraction caused by the objective lens28.

The laser beam reflected by the signal recording layer of the disc26(returning light) passes through the objective lens28, the reflecting mirror20, and the collimator lens22and then reaches the semitransparent mirror30. The laser beam having been transmitted through the semitransparent mirror30is given aberration by the AS plate34and then reaches the PDIC36. Thereafter, in the PDIC36, information is read, and focus servo and tracking servo are carried out based on the read information.

Next, description will be given of the second optical system42applied to discs of the DVD standard and the CD standard. Components of the second optical system42which are the same as those of the first optical system40will not be described.

The second optical system42includes the laser device39, diffraction grating33, the semitransparent mirror32, collimator lens27, reflecting mirror24, objective lens29, and the PDIC37.

The read/write operations of the disc26in the second optical system42are performed as follows. First, a laser beam of the CD standard or the DVD standard is emitted by the laser device39. The laser beam having been emitted by the laser device39passes through the diffraction grating33and is then reflected by the semitransparent mirror32. The laser beam is then transmitted through the collimator lens27, is then reflected by the reflecting mirror24so that the laser beam can proceed in a direction perpendicular to the information recording layer of the disc26, and is then focused on the information recording layer of the disc26by the objective lens29.

The laser beam having been reflected by the information recording layer of the disc26, i.e., returning light, passes through the objective lens29, is then reflected by the reflecting mirror24, is then transmitted through the collimator lens27and the semitransparent mirror32, and is then incident on a light-receiving surface of the PDIC37. Thereafter, in the PDIC37, information is read, and focus servo and tracking servo are carried out based on the read information.

Note that, not all the optical elements described above are essential. For example, the first optical system40may be formed only of the laser device38, the semitransparent mirror30, the collimator lens22, the objective lens28, and the PDIC36. Further, the PDIC36may be built in the laser device38. The same applies to the second optical system42. The second optical system42may be formed of the laser device39, the semitransparent mirror32, the PDIC37, the collimator lens27, the reflecting mirror24, and the objective lens29.

The configuration of the optical element moving device11will be described with reference toFIGS. 3A and 3B.FIG. 3Ais a perspective view showing a magnified portion of the optical element moving device11, andFIG. 3Bis a cross-sectional view taken along the line B-B′ ofFIG. 3A.

The optical element moving device11includes: the screw-shaped feed shaft44placed parallel with the optical path of a laser beam; the guide shafts46and48placed parallel with the feed shaft44; the element holding device50moving along the guide shafts46and48while holding the collimator lens22; and the wire52fixed on the element holding device50and wound toward the feed shaft44.

The feed shaft44is made by forming a helical thread groove at a predetermined pitch in an outer peripheral surface of a rod-shaped member made of metal such as stainless steel, brass, or free-cutting steel. The feed shaft44is placed in such a manner that its axis is directed parallel with a laser beam passing through the collimator lens22. The feed shaft44has a +X direction-side end connected to the stepping motor54and a −X direction-side end held rotatably. The stepping motor54is driven with a drive signal sent from the outside, and the feed shaft44is rotated by a predetermined amount by a drive force of the stepping motor54.

The guide shaft46is a rod-shaped member made of metal such as stainless steel. The guide shaft46has an intermediate portion inserted in a hole portion of the element holding device50, a +X direction-side end housed in a housing portion56constituting a portion of the housing12, and a −X direction-side end housed in a housing portion58. The two ends of the guide shaft46are fixedly attached to the respective housing portions56and58with an adhesive.

Convex portions60are each made by protruding the bottom surface portion15of the housing12in the +Z direction. The convex portions60are placed below the guide shaft46at positions on the +X side and −X side respectively of the element holding device50. Referring toFIG. 3B, even when a +X-side end of an insertion portion50A of the element holding device50is moved in the +X direction to bump into the corresponding convex portion60and stop, an extra-pulse is applied to the feed shaft44and thereby origin detection being a reference for determining the amount of movement of the element holding device50(the collimator lens22) is performed. Similarly, even when a −X-side end of the insertion portion50A of the element holding device50is moved in the −X direction to bump into the corresponding convex portion60and stop, an extra-pulse is applied to the feed shaft44and thereby origin detection being a reference for determining the amount of movement of the element holding device50(the collimator lens22) is performed.

The guide shaft48is made by forming a portion of the housing12in the form of a shaft, and a guide portion50D of the element holding device50engages with the guide shaft48. To put it differently, the guide shaft48is made by allowing a portion of the sidewall portion13of the housing12to protrude in the −Y direction to extend continuously in the X directions. Note that, although the guide shaft48may be made separately from the housing12as in the case of the guide shaft46, forming the portion of the housing12into the guide shaft48brings about an effect of reduction of components.

The feed shaft44and the guide shafts46and48are placed parallel with one another when viewed in the Z directions.

The element holding device50has the principal surface on/through which a laser beam is incident/transmitted and configured to hold the collimator lens22facing the X directions, a −Y direction-side edge portion in which to insert the guide shaft46, and a +Y direction-side edge portion engaging with the guide shaft48. With this configuration, the element holding device50is housed in the housing12to be movable in the X directions. The structure of the element holding device50will be described later with reference toFIGS. 4A and 4B.

The wire52is placed at a side surface of a −Y direction (a direction toward the feed shaft44) side edge portion of the element holding device50. A side surface of an end portion of the wire52is in contact with the thread groove of the feed shaft44. This feature will be described later with reference toFIGS. 4 and 5.

Spherical aberration is corrected by moving the optical element moving device11of the above configuration in the X directions. As has been described above, spherical aberration caused by a cover layer of an optical disc is different according to the standard of the disc; further, spherical aberration caused in an optical disc of the BD standard having multiple information recording layers is different from one information recording layer to another. Even in these cases, it is possible to correct such spherical aberration and to focus a laser beam on the target information recording layer properly by allowing the optical element moving device11to move the collimator lens22to a predetermined position.

With reference toFIGS. 4 to 7, description will be given of the element holding device50incorporated in the optical pickup apparatus10and the optical element moving device11.

The configuration of the element holding device50will be described with reference toFIGS. 4A and 4B.FIG. 4Ais an overall perspective view of the element holding device50, andFIG. 4Bis a cutaway perspective view of a wire fixing portion50E.

Referring toFIG. 4A, the element holding device50includes, in the following order starting from the +Y direction side: the guide portion50D engaging with the guide shaft48; a lens fixing portion50C on which to fix the collimator lens22; an arm portion50B; the insertion portion50A having a hole portion50H in which to insert the guide shaft46; and the wire fixing portion50E made by protruding a side surface of the insertion portion50A in the −Y direction. In this respect, the element holding device50is roughly in the faun of the alphabet “J” when viewed in the Z directions. The element holding device50is formed integrally by injection molding or casting of a resin material such as PPS or metal such as Al.

More specifically, the guide portion50D is in the form of a groove (the letter “U”) which is open in the +Y direction. The element holding device50is moved in the X directions by allowing this portion to engage with the guide shaft48shown inFIG. 3A.

The lens fixing portion50C has an opening to which the collimator lens22having a lens surface in the X directions (an axis direction of the collimator lens) is fixedly attached.

The arm portion50B has one end connected to the lens fixing portion50C and the other end connected to the insertion portion50A. Connecting the insertion portion50A and the lens fixing portion50C to each other through the arm portion50B makes it possible to place the lens fixing portion50C for fixing the collimator lens22at a predetermined position inside the optical pickup apparatus10regardless of space limitations.

The insertion portion50A is in the form of a rectangular solid which is long in the X directions, and has a −X direction-side end portion (a side surface perpendicular to the optical axis direction and its vicinity) connected to the lens fixing portion50C through the arm portion50B. In addition, the insertion portion50A has the hole portion50H cylindrically penetrating the insertion portion50A in the X directions. When in use, the guide shaft46shown inFIG. 3Ais inserted in the hole portion50H.

The wire fixing portion50E is made by cylindrically protruding a portion near a central portion of a −Y direction-side side surface of the insertion portion50A integrally in the −Y direction. In this respect, the −Y direction-side surface of the insertion portion50A is parallel with the optical axis and located on a side opposed to a side where the collimator lens is placed. The wire fixing portion50E is configured to fix the wire52, which is wound in the form of a coil, on the element holding device50with the wire52inserted on the wire fixing portion50E.

In this embodiment, the insertion portion50A and the lens fixing portion50C are connected to each other through the arm portion50B. This configuration can make the insertion portion50A and the lens fixing portion50C farther from each other than a configuration where the lens fixing portion50C is directly connected to the insertion portion50A. In addition, the arm portion50B has a lateral width smaller than those of the lens fixing portion50C and the insertion portion50A. With this configuration, even if vibration acts on the insertion portion50A when the element holding device is in use, the vibration is reduced by the arm portion50B and hence the reduced vibration acts on the lens fixing portion50C. Incidentally, the element holding device50may have a shape other than the shape described above. Other shapes will be described concretely later with reference toFIGS. 8A and 8B.

Referring toFIG. 4B, the wire52includes, in the following order starting from the +Y direction side (insertion portion side): a linear portion52B; a wound portion52A; a linear portion52C; a contact portion52D; and a bent portion52E. The wire52is formed by bending a wire. The wire52may be made of metal such as SUS or piano wire. The linear portion52B is made by linearly forming a +Y direction-side end portion of the wire52in such a way that the end portion passes through the center of the wound portion52A when the wire52is viewed in the Y directions. Similarly, the contact portion52D and the linear portion52C are each linearly formed to pass through the center of the wound portion52A when the wire52is viewed in the Y directions. Accordingly, when the wire52is viewed in the Y directions, the contact potion52D, the linear portion52C, and the linear portion52B substantially overlap one another. In addition, the linear portion52C and the contact portion52D are connected to each other through a portion which is bent in the form of the letter “U” at their lower ends. The wound portion52A is made by helically winding the wire52, and is formed to connect the lower end of the linear portion52B and the upper end of the linear portion52C to each other.

To put it differently, the wire52may be regarded as a spring. Specifically, the wound portion52A of the wire52is a coil spring having an axis directed in the Y directions, and a portion of the wire52located on the −Y side of the wound portion52A (i.e., the linear portion52C, the contact portion52D, and the bent portion52E) is a torsion spring. Although the wire52is wound circularly in this embodiment, the wire52may be wound in the form of a polygon such as a triangle or a rectangle.

In this embodiment, the wire52has, at a position near its −Y-side (an end surface protruding from the insertion portion) end, the bent portion52E made by bending an end portion of the contact portion52D at right angle in the +Y direction. With this configuration, when the wire52is inserted onto the wire fixing portion50E, the bent portion52E of the wire52is housed in a slit50G and thereby fixed therein. Thus, unwanted deformation of the contact portion52D can be prevented and the degree of deformation can be optimized according to the diameter and type of the wire. This feature will be described later with reference toFIGS. 5 and 6.

The wire fixing portion50E is substantially cylindrical, and has the slit50G which divides the wire fixing portion50E at its central portion. In addition, lock portions50F are formed by protruding two −Y direction-side edges of an outer peripheral portion of the wire fixing portion50E respectively in the +X and −X directions. InFIG. 4A, left and right semicircular portions made by division by the slit can be observed on a circular surface opposed to a surface where the wire fixing portion50E and the insertion portion50A are coupled to each other. The lock portions50F are provided to these semicircular portions respectively. The diameter of the wire fixing portion50E is set to be slightly smaller than the inner diameter of the wound portion52A of the wire52. Further, the −Y-side side surface of each lock portion50F is a sloping surface where a −Y-side end is located inside the opposite end. In other words, the lock portion50F is getting thicker from the −Y-side end toward the opposite end. This sloping surface allows the wire52to be easily fitted in the wire fixing portion50E.

Referring toFIG. 5, once the wound portion52A of the wire52is fitted in the wire fixing portion50E of the above configuration, portions of the wire52located at −Y direction-side end portions of the wound portion52A are locked by the two lock portions50F, whereby the wire52can be prevented from coming off from the wire fixing portion50E. In addition, the linear portions52B and52C and a portion at and near a leading end of the bent portion52E of the wire52are housed in the slit50G of the wire fixing portion50E, whereby the wire52is fixed to be immovable in its rotation direction and thus the contact portion521is kept substantially parallel with the Z directions. In other words, excess deformation of the wire52at a lower end of the contact portion52D can be suppressed (seeFIG. 4B). Further, the contact portion52D of the wire52is not housed in the slit50G but placed to protrude in the −Y direction (toward the feed shaft44shown inFIG. 3A) more than a −Y-side end of the wire fixing portion50E.

With reference toFIGS. 6A and 6B, description will be given of the configuration where the wire52is in contact with the feed shaft44.FIG. 6Ais a view showing a state where the wire52is biased toward the feed shaft44, andFIG. 6Bis a view showing the configuration where the contact portion52D of the wire52is in contact with the feed shaft44.

Referring toFIG. 6A, when the feed shaft44and the element holding device50are incorporated in the optical pickup apparatus10, the wire52is interposed between the element holding device50and the feed shaft44while being slightly compressed in the Y direction (in the direction toward the feed shaft). Accordingly, the contact portion52D is in contact with a thread groove44A of the feed shaft44while being pressed thereagainst by a bias force generated by the compression of the wound portion52A. The bias force is set within a range such that a rotation force of the feed shaft44can be transmitted to the element holding device50and that the contact portion52D would not be plastic deformed (i.e., in a range below the elastic limit), e.g., approximately 3 gf or larger and 15 gf or smaller.

When the feed shaft44is rotated by a drive force of the stepping motor54, a rotation force of the feed shaft44is transmitted to the element holding device50through the contact portion52D of the wire52, which slides on and in contact with the thread groove44A. Thereby, the element holding device50is moved in the X directions by a predetermined amount.

In this embodiment, the bent portion52E and bent portion52E′ being leading end portions of the wire52are housed in the slit50G. With this configuration, when the feed shaft44is rotated and a force to move the wire52in the +X direction acts on the wire52, the bent portion52E is brought into contact with a +X-side sidewall of the slit50G, whereby excess deformation of the contact portion52D can be suppressed.

Referring toFIG. 6B, the side surface of the contact portion52D of the wire52is in contact with two side surfaces of the thread groove44A, which are included in one pitch, at two points. A bias force F to be applied on the thread groove44A by the contact portion52D through the two contact points is a substantial bias force to be applied on the feed shaft44by the contact portion52D.

With reference toFIGS. 7A to 7C, description will be given of the contact portion52D provided to the leading end of the wire52.FIGS. 7A and 7Bare perspective views each showing a case where no bent portion52E is provided, andFIG. 7Cis a perspective view showing this embodiment where the bent portion52E is provided.

As has been described with reference toFIGS. 4 and 5, excess deformation of the wire52at the lower end of the contact portion52D is prevented in this embodiment by placing the bent portion52E being the leading end portion of the wire52in the slit50G. This feature will be described below.

Referring toFIG. 7A, assuming that the bent portion52E is not provided, the movement of an upper end portion of the contact portion52D is not restricted. Even in this case, when the feed shaft44is rotated by the drive force of the stepping motor54, the rotation force of the feed shaft44is transmitted to the insertion portion50A through the wire52because the contact portion52D is in contact with the thread groove44A of the feed shaft44, whereby the element holding device50is moved in the X directions.

However, if the contact portion52D has the free end as described above, failure occurs in which the wire52is excessively deformed at a portion of the contact portion52D as shown inFIG. 7B. More specifically, referring toFIG. 3B, if the stepping motor54keeps the feed shaft44rotated even after the rotation of the feed shaft44makes the element holding device50bump into one of the convex portions60for origin detection, the contact portion52D is sometimes stressed and deformed as shown inFIG. 7B. The state where the contact portion52D is stressed may adversely affect the following operation of the element holding device50.

As a countermeasure against this, in this embodiment, the bent portion52E is made by bending the upper end portion of the contact portion52D in the +Y direction, and the bent portions52E and52E′ thus made are housed in the slit50G as shown inFIG. 7C.

Thereby, the contact portion52D protrudes in the −Y direction more than the wire fixing portion50E in order to contact the feed shaft44, whereas the bent portions52E and52E′ are inserted in the slit50G. Thus, excess deformation of the contact portion52D in the ±X directions is restricted by the slit50G while the contact portion52D can be deformed in the Y directions.

With the above configuration, excess deformation of the contact portion52D is suppressed. Specifically, as shown inFIG. 3B, if the rotation force is kept applied on the wire52even after the rotation of the feed shaft44makes the element holding device50bump into one of the convex portions60, a force to deform the contact portion52D is applied on the wire52. In this embodiment, since the bent portions52E and52E′ are housed in the slit50G, these portions function to suppress deformation of the contact portion52D. Accordingly, excess deformation of the contact portion52D is suppressed and no stress remains in the contact portion52D. This makes smooth the subsequent operation of the element holding device50.

Further, although the element holding device50shown inFIGS. 4A and 4Bholds the collimator lens22according to the above description, the element holding device50may hold an optical element other than the collimator lens22. For example, the element holding device50of this embodiment may hold a lens to be placed inside an optical camera having an autofocus function.

Furthermore, although the element holding device50shown inFIGS. 4A and 4Bis in the form of the alphabet “J” in a plan view, the element holding device50may have another shape. Element holding device50of another embodiment will be described with reference toFIGS. 8A and 8B.FIGS. 8A and 8Bare perspective views each showing the element holding device50of another embodiment.

Referring toFIG. 8A, an arm portion50B is connected at right angle to one longitudinal end of an insertion portion50A. The insertion portion50A and a lens fixing portion50C are connected to each other through the arm portion50B. In this case, the element holding device50is in the form of the alphabet “L” in a plan view. In this respect, the lens fixing portion50C may be connected directly to the insertion portion50A without the arm portion50B.

In the element holding device50shown inFIG. 8B, arm portion50B is connected to an intermediate portion of a side surface of insertion portion50A at right angle with respect to the longitudinal direction of the insertion portion50A. In this case, the element holding device50is in the form of the alphabet “T.”

It should be noted that the shapes of the element holding device50described above are merely an example, and the element holding device50may have another shape as long as the relative positional relationship between the lens fixing portion50C and the insertion portion50A is kept.

Another embodiment of the element holding device50will be described with reference toFIG. 9. In this embodiment, a contact portion52D provided to a leading end portion of wire52is not housed in slit50G but placed on a −Y side of an end of wire fixing portion50E. The element holding device50of such a configuration can bring about a similar effect to those of the above holding devices50.

According to the present invention, since the element holding portion configured to hold the optical element in such a way that the element is movable is in contact with the feed shaft through the wire. This achieves the configuration without the nut which has been described in the description of the related art, and suppresses noise and vibration which have been heretofore caused by the employment of the nut.

Further, as compared with the conventional apparatus using the nut, the present invention eliminates the need of components in contact with a nut, a spring to remove backlash, and the like. This reduces the number of components, and thus simplifies the structure and improves the reliability.

Furthermore, according to the present invention, a portion of the wire is housed in the housing area provided to the leading end portion of the fixing portion configured to fix the wire. This restricts the movement of the leading end portion of the wire, and thus suppresses unexpected deformation of the wire.