Patent Publication Number: US-2007109632-A1

Title: Optical pickup apparatus

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an optical pickup apparatus for recording/reproducing various information onto/from an information recording medium such as a CD or a DVD, particularly in which the assembling structure of a grating to be incorporated for generation of a focusing error signal and/or a tracking error signal is improved.  
      2. Description of the Prior Art  
      In general, the optical system of optical pickup apparatuses is basically composed of: a columnar LD (Laser Diode) for emitting a laser beam; a columnar resin grating for diffracting the laser beam from the LD; an objective lens for focusing the diffracted light from the grating on an optical disk; and a photodetector for receiving the returning light from the optical disk through the objective lens. Among these components, the LD and grating are assembled onto a base portion that constitutes a part of the optical pickup apparatus main body to form an integrated light source unit from the viewpoint of mainly stabilizing the emitting direction of the laser beam (diffracted light).  
      In the case above, in order that the positions of the optical components can be adjusted mutually, the grating is attached to the base portion in such a manner, for example, as to be movable in the optical axis direction of the laser beam and rotatable around the optical axis, and then is fixed to the base portion by adhesive, etc. after the position in the optical axis direction and the rotational position are adjusted. Here, Japanese Patent Laid-Open Publication No. 2000-285494 discloses an optical pickup apparatus having a mechanism capable of adjusting the phase of a grating for diffracting an emitted laser beam easily and precisely.  
      Specifically, in an optical pickup apparatus having: a grating for diffracting a laser beam emitted from a laser light source; a holder to which the grating is fixed; a housing portion in an apparatus frame in which the holder is housed movably; and a coil spring pressing and fixing the holder against the housing portion, a spacer is sandwiched between the holder and the coil spring.  
      Then, in this configuration, the spacer prevents the coil spring from coming into contact with the holder, whereby the elastic restoring force of the coil spring cannot be transferred to the holder and it can also be prevented that the end of the coil spring is caught in irregularities on the end face of the holder. This therefore results in allowing adverse effects due to the coil spring to be prevented.  
      However, allowing for such a phase adjustment requires at least a spacer and a coil spring separately, resulting in a problem of forcing complicated parts control and/or assembly operations as well as of insufficiently responding to the requirement of cost reduction. Hence, Japanese Patent Laid-Open Publication No. 2004-22034 discloses an optical pickup apparatus whereby the phase of a grating can be adjusted sufficiently while reducing the number of parts to suppress complicated parts control and/or assembly operations as well as to respond to the requirement of cost reduction.  
      Specifically, in an optical pickup apparatus having a housing recessed portion in which a columnar grating for diffracting a laser beam, an elastic body for pressing the grating in the axial direction, and an LD for supporting the elastic body and for emitting the laser beam are inserted in this order, the elastic body is formed by integrally molding a plate-like portion formed with a through hole for passing the laser beam therethrough and in contact with the front surface of the grating and a plurality of protruding pieces protruding symmetrically from the edge portion of the plate-like portion to be deformed elastically and brought into contact with the front surface of the LD.  
       FIG. 6  is a disassembled plan view showing an example of the mounting structure of a grating in such a conventional optical pickup apparatus having an elastic body formed by integrally molding a plate-like portion and protruding pieces. In this figure, the numeral  101  indicates a base generally composed of molded parts by die-casting, etc. on which a plurality of optical components of the optical pickup apparatus such as a beam splitter and various lenses are mounted. However, the plurality of optical components are not shown in the figure.  
      In the front part of the base  101 , there is provided a recessed portion  101   a , in which an approximately columnar grating  102  is inserted. G spring  103  corresponding to the above-described elastic body is incorporated concentrically from the front of the grating  102  and further is pressed and fixed by an LD spring  104  from the front thereof. The LD spring  104  is a sheet metal part having an approximately U shape when viewed from side, into which a holder not shown in the figure is to be fitted. An LD not shown in the figure is held in the holder and is arranged concentrically with the grating  102  and G spring  103 .  
      The G spring  103  is made from a metal plate such as SUS and, as shown in the front and plan views of FIGS.  7 ( a ) and  7 ( b ), is formed by integrally molding an annular plate-like portion  103   a  having an outside diameter approximately the same as the diameter of the grating  102  and formed with a through hole “h” for passage of laser beams through the center axis and a pair of protruding pieces  103   b  protruding from the edge portion of the plate-like portion  103   a  in a bent manner. Therefore, each protruding piece  103   b  is to be deformed elastically by loading in the axial direction with respect to the plate-like portion  103   a  to serve as a so-called plate spring.  
      Meanwhile, the grating  102  is adapted to diffract a laser beam transmitting through the vicinity of the center axis thereof, and a groove for inserting therein an adjusting jig for phase adjustment is formed in the outer peripheral surface of the grating  102  in the axial direction (not shown in the figure).  FIG. 8  is a view showing an example of such an adjusting jig, where  FIG. 8 ( a ) is a front view and  FIG. 8 ( b ) is a bottom view. The adjusting jig  105  has a rod shape including a relatively thick grip portion  105   a  and rods  105   b  and  105   c  extending from the grip portion while getting thin by two steps, and an eccentric pin  105 d is provided at the leading end of the rod  105   c.    
      Referring again to  FIG. 6 , the protruding pieces  103   b  of the G spring  103  are deformed elastically with the foregoing components being mounted on the base  101  so that the leading end portions thereof are brought into contact with the LD spring  104  and that the plate-like portion  103   a  is brought into contact with the grating  102 , whereby the elastic forces of the protruding pieces  103   b  are applied to the grating  102  in the axial direction. Therefore, the grating  102  is pressed against the bottom surface of the recessed portion  101   a  so that the axial movement thereof is restricted and is held rotatably around the axis, which allows for phase adjustment.  
      Then, the phase adjustment is achieved by inserting the above-described rod-shaped adjusting jig  105  into a through hole  101   b  that penetrates from the upper surface of the base  101  to the recessed portion  101   a , inserting the eccentric pin  105   d  into the foregoing groove in the grating  102 , and rotating the adjusting jig  105  directly to swivel the eccentric pin  105   d  so that the grating  102  is rotated around the axis. In this case, the grating  102  and the plate-like portion  103   a  are in contact with each other and slide smoothly against each other, where the plate-like portion  103   a  and the grating  102  have approximately the same diameter, which makes it possible to keep a uniform contact state and also stabilizes the mutual sliding therebetween.  
      In addition, an approximately flat plate-like cover  106  is fixed to the upper surface of the base  101 . This is achieved by fitting and positioning a positioning hole  106   a  opened at a corner of the cover  106  against a positioning pin  101   c  protruding from the upper surface of the base  101  and then screwing a screw  107  into a screw hole  101   d  provided in the vicinity of the positioning pin  101   c  through a fitting hole  106   b  provided in the vicinity of the positioning hole  106   a . This allows the cover  106  to be fixed onto the upper surface of the base  101 .  
      However, such a conventional arrangement as shown in  FIG. 6  still requires an elastic member (G spring  103 ) for urging a grating and forces complicated assembly operations such as fixing an LD while holding the elastic member by the hands of an operator, resulting in poor productivity.  
     SUMMARY OF THE INVENTION  
      The present invention has been made in consideration of the above-described problems, and an object thereof is to provide an optical pickup apparatus whereby the phase of a grating can be adjusted sufficiently even while further reducing the number of parts.  
      In order to achieve the foregoing object, the present invention is directed to an optical pickup apparatus including: a base having a cover; a grating for diffracting a laser beam; a housing recessed portion provided in the base to house the grating movably; and an elastic body for pressing and fixing the grating against the housing recessed portion, wherein the elastic body is molded integrally with the cover.  
      Also, the elastic body is characterized by including: an annular plate-like portion having an outside diameter approximately the same as the diameter of the grating and in contact with the grating; and a connecting portion for connecting the edge portion of the plate-like portion and the end portion of the cover.  
      Alternatively, the elastic body is characterized by including: a U-shaped plate-like portion having a width approximately the same as the diameter of the grating with the leading ends thereof being in contact with the grating; and a connecting portion for connecting the edge portion of the plate-like portion and the end portion of the cover.  
      In accordance with the present invention, it is possible to provide an optical pickup apparatus whereby the phase of a grating can be adjusted sufficiently even while further reducing the number of parts.  
      Specifically, the assembly operations are facilitated while reducing the number of parts by molding the elastic body for pressing the grating in the axial direction integrally with the cover of the base, and further the optical pickup apparatus whereby the phase of the grating can be adjusted sufficiently is achieved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic block diagram showing the optical system of an optical pickup apparatus according to the present invention;  
       FIG. 2  is a view showing the mounting structure of a grating in an optical pickup apparatus according to a first embodiment of the present invention;  
       FIG. 3  is a view showing the shape of a cover according to the first embodiment;  
       FIG. 4  is a view showing the mounting structure of a grating in an optical pickup apparatus according to a second embodiment of the present invention;  
       FIG. 5  is a view showing the shape of a cover according to the second embodiment;  
       FIG. 6  is a disassembled plan view showing an example of the mounting structure of a grating in a conventional optical pickup apparatus;  
       FIG. 7  is a view showing the shape of a G spring as a conventional elastic body; and  
       FIG. 8  is a view showing an example of an adjusting jig. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Embodiments of the present invention will hereinafter be described with reference to the accompanying drawings.  
       FIG. 1  is a schematic block diagram showing the optical system of an optical pickup apparatus according to the present invention. As shown in this figure, the optical system of the optical pickup apparatus  1  is composed of: a light source unit  4  including an LD (Laser Diode)  2  and a grating  3 ; a beam splitter  5  such as a half mirror or a prism for reflecting a laser beam (diffracted light) emitted from the light source unit  4  toward an optical disk  10  and for transmitting returning light from the optical disk  10  therethrough; a collimator lens  6  for converting the reflected light from the beam splitter  5  into parallel light; an objective lens  7  for focusing the parallel light from the collimator lens  6  on the recording surface of the optical disk  10 ; and a photodetector  9  for receiving the returning light from the optical disk  10  through the beam splitter  5  and a sensor lens  8 .  
     First Embodiment  
       FIG. 2  is a view showing the mounting structure of a grating in an optical pickup apparatus according to a first embodiment of the present invention, where  FIG. 2 ( a ) is a plan view,  FIG. 2 ( b ) is a front view, and  FIG. 2 ( c ) is a side view.  FIG. 2 ( a ) shows a base seen through a cover. Also, FIGS.  2 ( b ) and  2 ( c ) show only a cover and a grating. In this figure, the numeral  11  indicates a base generally composed of molded parts by die-casting, etc. on which a plurality of optical components of the optical pickup apparatus such as a beam splitter and various lenses are mounted. However, the plurality of optical components are not shown in the figure.  
      In the front part of the base  11 , there is provided a recessed portion, in which an approximately columnar grating  3  is inserted. Also, an approximately flat plate-like cover  12  made from a metal plate such as SUS is fixed to the upper surface of the base  11 . This is achieved by screwing a screw not shown in the figure into a screw hole  11   a  provided in the upper surface of the base  11  through a fitting hole  12   a  opened at a corner of the cover  12 . This allows the cover  12  to be fixed onto the upper surface of the base  11 . The positional relationship between the grating  3  and an LD not shown in the figure is the same as in the above-described conventional arrangement.  
      Now, in the present embodiment, a plate spring portion  12   b  formed in a bent manner is provided in the front part of the cover  12 . The plate spring portion is composed of an annular plate-like portion  12   ba  having an outside diameter approximately the same as the diameter of the grating  3  and formed with a through hole “h” for passage of laser beams through the center axis and a connecting portion  12   bb  for connecting the edge portion of the plate-like portion  12   ba  and the front end of the cover  12 . Therefore, the connecting portion  12   bb  is to be deformed elastically by loading in the axial direction with respect to the plate-like portion  12   ba  to serve as a so-called plate spring.  
      Meanwhile, the grating  3  is adapted to diffract a laser beam transmitting through the vicinity of the center axis thereof, and a groove for inserting therein an adjusting jig for phase adjustment is formed in the outer peripheral surface of the grating  3  in the axial direction (not shown in the figure). The adjusting jig to be used is the same as shown in  FIG. 8 . As for the plate spring portion  12   b , the connecting portion  12   bb  is deformed elastically and the plate-like portion  12   ba  is in contact with the grating  3 , whereby the elastic force of the connecting portion  12   bb  is applied to the grating  3  in the axial direction.  
      Therefore, the grating  3  is pressed against the bottom surface of the recessed portion not shown in the figure, which is provided in the base  11 , so that the axial movement thereof is restricted and is held rotatably around the axis, which allows for phase adjustment. Then, the phase adjustment is achieved by inserting the above-described adjusting jig into a hole  12   c  that is provided in the front part of the cover  12  and into a notch portion  11   b  that is provided at the front end of the base  11 , inserting the eccentric pin into the foregoing groove in the grating  3 , and rotating the adjusting jig directly to swivel the eccentric pin so that the grating  3  is rotated around the axis.  
      In this case, the grating  3  and the plate-like portion  12   ba  are in contact with each other and slide smoothly against each other, where the plate-like portion  12   ba  and the grating  3  have approximately the same diameter, which makes it possible to keep a uniform contact state and also stabilizes the mutual sliding therebetween. Here, the shape of the cover  12  is shown in  FIG. 3 , where  FIG. 3 ( a ) is a plan view,  FIG. 3 ( b ) is a front view, and  FIG. 3 ( c ) is a side view.  
     Second Embodiment  
       FIG. 4  is a view showing the mounting structure of a grating in an optical pickup apparatus according to a second embodiment of the present invention, where  FIG. 4 ( a ) is a plan view,  FIG. 4 ( b ) is a front view, and  FIG. 4 (c) is a side view.  FIG. 4 ( a ) shows a base seen through a cover. Also, FIGS.  4 ( b ) and  4 ( c ) show only a cover and a grating. The basic configuration of the present embodiment is the same as that of the above-described first embodiment, except that the shape of a plate spring portion to be provided in the front part of the cover is different.  
      Now, in the present embodiment, a plate spring portion  12   d  formed in a bent manner is provided in the front part of the cover  12 . The plate spring portion is composed of a U-shaped plate-like portion  12   da  having a width approximately the same as the diameter of the grating  3  and formed with an opening “o” for passage of laser beams through the center thereof and a connecting portion  12   db  for connecting the edge portion of the plate-like portion  12   da  and the front end of the cover  12 . Therefore, the connecting portion  12   db  is to be deformed elastically by loading in the axial direction with respect to the plate-like portion  12   da  to serve as a so-called plate spring.  
      The leading ends of the plate-like portion  12   da  are bent into an approximately V shape when viewed from side, the bent portions being adapted to press approximately the center of the grating  3  when viewed from side. Thus, the grating  3  is pressed approximately uniformly against the bottom surface of the recessed portion not shown in the figure, which is provided in the base  11 , so that the axial movement thereof is restricted and is held rotatably around the axis, which allows for stable phase adjustment.  
      Further, since the leading ends of the plate-like portion  12   da  are bent, the leading ends of the plate-like portion  12   da  cannot be caught on the grating  3  even when slid as indicated by the arrow in  FIG. 4 ( c ) to fit the cover  12  to the base  11 . Here, the shape of the cover  12  is shown in  FIG. 5 , where  FIG. 5 ( a ) is a plan view,  FIG. 5 ( b ) is a front view,  FIG. 5 ( c ) is a side view, and  FIG. 5 ( d ) is an auxiliary projection view of the plate spring portion.  
      As described heretofore, in accordance with the present invention, the assembly operations are facilitated while reducing the number of parts by molding the elastic body for pressing the grating in the axial direction integrally with the cover of the base, and further the optical pickup apparatus whereby the phase of the grating can be adjusted sufficiently is achieved.