Abstract:
In an optical pickup, it is configured such that a first and a second thrust bearings of a motor rotation shaft, a lens holder to be moved in a thrust direction by the motor rotation shaft, and a preload unit which exerts preload of the thrust direction on the lens holder are included, and the second thrust bearing can adjust a position in the thrust direction. In addition, the first and second thrust bearings and the motor rotation shaft are made of conductor, and the optical pickup is manufactured by including the processes of: moving the second thrust bearing in a direction approaching to the motor rotation shaft till electrical continuity between the first thrust bearing and the second thrust bearing is obtained using an electrical continuity checker; subsequently moving the second thrust bearing in a direction departing from the motor rotation shaft; and subsequently fixing the second thrust bearing to the base.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an optical pickup for use in an optical disk device which records information on a recording surface of an optical disk and/or reproduces information recorded thereon. 
         [0003]    2. Description of the Related Art 
         [0004]    As correction means of spherical aberration for an optical disk, there is known means for correcting spherical aberration by moving a lens in an optical axis direction. 
         [0005]    For example, Japanese Patent Application Laid-Open No. 2006-155839 discloses a configuration in which motor&#39;s rotating motion is converted into linear motion in a thrust direction and both a lens holder which abuts on a nut and a lens which is supported by and fixed to a lens holder are moved in an optical axis direction, by a screw mechanism which is combined by a lead screw formed on a motor rotation shaft and a nut engaged with the lead screw. As described above, in the configuration which obtains linear motion in the thrust direction by the screw mechanism, a backlash of the motor rotation shaft in the thrust direction can make a cause of vibration. In Japanese Patent Application Laid-Open No. 2006-155839, preload is exerted by a coil spring to bring the lens holder into contact with the nut. The preload is exerted in the order corresponding to the nut, the lead screw engaged with the nut, and the motor rotation shaft which fixes the lead screw, to bring the motor rotation shaft into contact with a thrust bearing provided at one end of the motor rotation shaft. As described above, there is the configuration that suppresses the backlash in the thrust direction by the preload. 
         [0006]      FIG. 1  in Japanese Patent Application Publication No. 60-11536 discloses a configuration in which, in a mechanism that decelerates rotational speed of a motor rotation shaft by a worm gear, an adjustment screw is assembled at a tip end position of the motor rotation shaft; thrust adjustment is made by the adjustment screw; and then, the adjustment screw is fixed by the nut. In such configuration, an amount of movement of the motor rotation shaft in a thrust direction can be adjusted without exerting preload, and therefore, a backlash which makes a cause of vibration can be reduced. 
         [0007]    In addition, Japanese Patent Application Laid-Open No. 2001-330027 discloses a configuration which can implement thrust adjustment at any time after assembling by providing display means for displaying an amount of movement of an adjustment screw in an axial direction of a rotation shaft. 
         [0008]    In the thus configured optical pickup, there is a case that, after the nut and the lens holder abut on a stopper provided to control the movement in the thrust direction and stop, the nut and the lens holder will not move even if driven in a reverse direction. This is caused by that, when the nut and the lens holder stop by the stopper, the motor rotation shaft moves in the thrust direction by a reaction force from the stopper and a rotor mounted to the motor rotation shaft come in contact with a side surface in a motor case due to the movement, and consequently, a large frictional force is generated. 
         [0009]    With respect to the above problems, in a configuration disclosed in Japanese Patent Application Laid-Open No. 2006-155839, it is possible to avoid that the motor rotor comes in contact with the side surface in the motor case, by increasing the preload of the coil spring to resist the reaction force from the stopper and to suppress the movement of the motor rotation shaft in the thrust direction. However, the preload of the coil spring continues to exert on each part during usual operation when reaction force from the stopper is not generated, and therefore, there is a possibility that movement in a reverse direction against the preload becomes difficult and there arise problems such as an increase in slide load and mechanical wear in a slide member such as a thrust bearing. 
         [0010]    Meanwhile, Japanese Patent Application Publication No. 60-11536 and Japanese Patent Application Laid-Open No. 2001-330027 disclose the configuration in which the amount of movement of the motor rotation shaft in the thrust direction is adjusted by clamping the adjustment screw and contact between the motor rotor and the side surface in the motor case can be avoided. However, when the amount of movement of the motor rotation shaft in the thrust direction is set to zero, both ends of the motor rotation shaft come in contact with the adjustment screw and a thrust bearing while exerting a force thereon, and therefore, a slide resistance is generated. When a temperature rise is generated in such contact conditions, the amount of movement in the thrust direction due to an expansion of the motor rotation shaft is narrowed, and therefore, a further large slide resistance is generated. The increase in slide resistance becomes a load to the motor and leads to a lowering in output torque. On the contrary, when the amount of movement in the thrust direction is secured in order to decrease the slide resistance, the preload means is not provided in this configuration, and therefore, vibration in the thrust direction is generated. In this configuration, the amount of movement in the thrust direction needs to be strictly controlled in order to balance the reduction in slide resistance and the reduction in vibration level, and therefore, there is a possibility of a hindrance to improving production efficiency. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention has been made to avoid contact between a motor rotor and a side surface in a motor case, and an object of the present invention is to provide an optical pickup in which a function that adjusts an amount of movement of a motor rotation shaft in a thrust direction is added to an optical pickup which had been enough by the configuration disclosed in Japanese Patent Application Laid-Open No. 2006-155839, and accordingly, a nut and a lens holder which stopped due to contact with a stopper are surely driven in a reverse direction and reliability is improved. 
         [0012]    As means for solving the above problem, the present invention is configured such that, in an optical pickup which includes: a motor having a rotation shaft; a first thrust bearing at one end of the motor rotation shaft; a second thrust bearing at the other end of the motor rotation shaft; a base which fixes a motor case of the motor; a lead screw fitted to the motor rotation shaft; a screw mechanism which converts rotation of the lead screw into linear motion; a lens holder to be moved in a thrust direction by the screw mechanism; a lens to be held by the lens holder; and preload means for exerting preload of the thrust direction on the lens holder, the second thrust bearing can adjust a position in the thrust direction. 
         [0013]    In addition, a first thrust bearing, a second thrust bearing, and a motor rotation shaft are made of conductor; and an optical pickup is manufactured by including the processes of: moving the second thrust bearing in a direction approaching to the motor rotation shaft till electrical continuity between the first thrust bearing and the second thrust bearing is obtained using an electrical continuity checker; subsequently moving the second thrust bearing in a direction departing from the motor rotation shaft; and subsequently fixing the second thrust bearing to the base. 
         [0014]    Further, an optical pickup is manufactured by including the processes of: inserting a spacer made of conductor between the motor rotation shaft and the first thrust bearing, or between the motor rotation shaft and the second thrust bearing; moving the second thrust bearing in a direction approaching to the motor rotation shaft till electrical continuity between the first thrust bearing and the second thrust bearing is obtained using an electrical continuity checker; subsequently removing the spacer; and fixing the second thrust bearing to the base. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a view showing a configuration of an optical pickup according to a first embodiment of the present invention; 
           [0016]      FIG. 2  is a view showing spherical aberration correction means of the optical pickup according to the first embodiment of the present invention; 
           [0017]      FIG. 3  is a view showing a method of manufacturing the spherical aberration correction means of the optical pickup according to the first embodiment of the present invention; and 
           [0018]      FIG. 4  is a view showing a method of manufacturing spherical aberration correction means of an optical pickup according to a second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     First Embodiment  
       [0019]    An optical pickup according to a first embodiment of the present invention will be described with reference to  FIGS. 1 to 3 . 
         [0020]      FIG. 1  is a view showing a configuration of the optical pickup according to the first embodiment of the present invention. 
         [0021]    In  FIG. 1 , reference numeral  1  denotes an optical disk,  2  denotes an optical pickup,  21  denotes a laser light source,  22  denotes a shaping lens,  23  denotes a coupling lens,  24  denotes a beam splitter,  25  denotes spherical aberration correction means,  26  denotes a reflecting mirror,  27  denotes an object lens,  28  denotes a detector lens, and  29  denotes a photo-detector. 
         [0022]    The optical pickup  2  mounts the laser light source  21 , the shaping lens  22 , the coupling lens  23 , the beam splitter  24 , the spherical aberration correction means  25 , the reflecting mirror  26 , the object lens  27 , the detector lens  28 , and the photo-detector  29  in one case; and constitutes an optical system which performs recording and reproducing of information on and from the optical disk  1 .  FIG. 1  shows the optical pickup  2  comprising one optical system, however, a plurality of optical systems may be mounted in one case in order to accommodate a plurality of standards on optical disk  1 . In this case, a configuration can be made such that a component is shared in different optical systems. The laser light source  21  is a laser diode which oscillates and emits laser light having a specific wavelength corresponding to CD, DVD, BD, or HD-DVD. The shaping lens  22 , the coupling lens  23 , the beam splitter  24 , the reflecting mirror  26 , the object lens  27 , and the detector lens  28  are optical lens or an optical mirror made of glass or transparent plastic. Functionality coating is applied to a lens surface and a reflection surface if required. The spherical aberration correction means  25  is formed by an optical lens made of glass or transparent plastic and a mechanism which moves the optical lens in an optical axis direction of the lens. The optical lens which constitutes the spherical aberration correction means  25  may be of a two lenses configuration by adding one fixed lens. The photo-detector  29  is a semiconductor device which generates a voltage corresponding to light intensity irradiating a photo detection surface. 
         [0023]    Laser light emitted from the laser light source  21  is made incident on the shaping lens  22  first. The shaping lens  22  is a lens which shapes laser light having an oval cross section, emitted from the laser light source  21 , to substantially a circular cross section. A curved surface is formed on a laser light incident surface and a laser light emitting surface of the shaping lens  22 . Next, laser light emitted from the shaping lens  22  is made incident on the coupling lens  23 . The coupling lens  23  has a function which converts the laser light diverged and emitted from the laser light source  21  into parallel light. The laser light converted into the parallel light is transmissive through the beam splitter  24  and reaches the spherical aberration correction means  25 . The spherical aberration correction means  25  has a driving mechanism of the lens and has a function which adjusts the laser light that has passed through the lens to weak divergent or weak convergent light by moving the lens in the optical axis direction. Further, the laser light is made incident on the object lens  27  via the reflecting mirror  26  and is collected on a recording surface of the optical disk  1  by the object lens  27  to form a beam spot. The optical pickup  2  performs recording and reproducing of information by the beam spot. In recording, on/off operation of the laser light source  21  is performed on the basis of recording information, and a recording pit is formed on the optical disk  1  by the beam spot to perform writing of information. In reproducing, laser light impinging upon the recording pit of the optical disk  1  and being reflected is picked up by the object lens  27 , and the laser light is introduced onto the detection surface of the photo-detector  29  via the reflecting mirror  26 , the spherical aberration correction means  25 , the beam splitter  24 , and the detector lens  28 , in the order reverse to a forward route. The photo-detector  29  detects returned light from the optical disk  1  at an internal detection surface and performs reading of information. In addition, it is configured such that focus control and tracking control of the object lens  27 , and lens position control of the spherical aberration correction means  25  are performed by processing a detection signal. 
         [0024]      FIGS. 2 and 3  show a configuration and a manufacturing method of the spherical aberration correction means  25  mounted on the optical pickup  2  according to the first embodiment of the present invention. 
         [0025]    In  FIGS. 2 and 3 , reference numeral  251  denotes a lens,  252  denotes a lens holder,  253  denotes a screw mechanism,  254  denotes preload means,  255  denotes a motor,  255   a  denotes a motor case,  255   b  denotes a rotation shaft,  255   c  denotes a lead screw,  255   d  denotes a first thrust bearing,  256  denotes a second thrust bearing,  257  denotes a base,  258  denotes a stopper,  259  denotes an assembly jig,  259   a  denotes a driver,  259   b  denotes an electrical continuity checker,  259   c  denotes a probe, and  259   d  denotes a bonding instrument. The spherical aberration correction means  25  is incorporated in the optical pickup  2  shown in  FIG. 1 . 
         [0026]    The spherical aberration correction means  25  is of a configuration in which the base  257  is mounted with the lens  251 , the lens holder  252 , and the screw mechanism  253  that are driven units; the motor  255  that is a power driver; and the preload means  254 , the second thrust bearing  256 , and the stoppers  258  that are peripheral members. The lens  251  is an optical lens made of transparent resin such as polyolefin with high transmittance, or glass. Correction of the spherical aberration is implemented by diverging and converging the laser light incident on the lens  251  by moving the lens  251  in the optical axis direction. The lens holder  252  has an aperture to hold the lens  251 , and the lens  251  is fixed by being fitted and adhered to the aperture. The lens holder  252  is suspended by a guiding shaft, and is configured so as to move in the optical axis direction of the lens  251  together with the lens  251 . The screw mechanism  253  is a nut or a claw formed with a female screw on its inner periphery. In the case where the screw mechanism  253  is formed by a nut as shown in  FIG. 2 , the nut is rotated together with rotation of the lead screw  255   c  to be engaged therewith, and therefore, a rotation stop (not shown in the drawing) needs to be provided. The rotation stop can be realized by forming a projection or a groove on the nut and making the same abut on the lens holder  252  or an external member. In the case where the screw mechanism  253  is configured by a claw, it may be a configuration that a claw member is made and the same is fixed to the lens holder  252 , or a configuration that the claw is directly formed on the lens holder  252 . The preload means  254  is a member such as a spring which exerts preload of the optical axis direction on the lens holder  252 . The motor  255  is a small size direct current motor or a stepping motor which can be mounted on the optical pickup  2 . The lead screw  255   c  with grooves formed at a constant pitch on its outer periphery is formed on the output side of the rotation shaft  255   b.  The lead screw  255   c  is formed by direct processing on the rotation shaft  255   b  of the motor  255 , or formed as a different part and then, fixed to the rotation shaft  255   b  by caulking or the like. In addition, the motor  255  has the first thrust bearing  255   d  which is formed at the shaft end on the opposite side to the output side of the rotation shaft  255   b.  The first thrust bearing  255   d  is a plate which stops movement of the rotation shaft  255   b  in a thrust direction. The second thrust bearing  256  is a screw or a pin which is engaged with the base  257  and mounted at the shaft end on the output side of the rotation shaft  255   b . The second thrust bearing  256  is a plate which stops movement of the rotation shaft  255   b  in the thrust direction. The second thrust bearing  256  has a function which adjusts a position in the thrust direction, and accordingly, an amount of movement of the rotation shaft  255   b  in the thrust direction is adjusted. The base  257  is a case of the spherical aberration correction means  25 , and is a member which fixes the motor case  255   a  and the second thrust bearing  256 . The base  257  is required to reduce weight in consideration of impact resistance for the optical pickup  2 , and therefore, resin is used. The present first embodiment is formed especially by resin which blocks electricity. This electrically insulates the first thrust bearing  255   d  from the second thrust bearing  256 . This insulation is a function necessary for improving productivity with a manufacturing method to be described later. The stopper  258  is a member which restricts an amount of movement of the lens holder  252  or the screw mechanism  253  in the thrust direction. 
         [0027]    Next, an operation of the spherical aberration correction element  25  will be described. The spherical aberration correction element  25  is driven by a motor  255 . The motor  255  rotates the rotation shaft  255   b  by generating a torque around the rotation shaft  255   b  by electromagnetic action by flowing a current through coils formed inside the motor. The rotation of the rotation shaft  255   b  makes the lead screw  255   c  rotate, so that the screw mechanism  253 , which performs linear motion along the groove of the lead screw  255   c,  moves in the thrust direction. The lens holder  252  conducts movement, constantly being abutted on the screw mechanism  253  by the preload means  254 , and accordingly, the lens  251  is moved in the optical axis direction. The amount of movement of the lens holder  252  and the screw mechanism  253  in the thrust direction is restricted by the stoppers  258 . When the lens holder  252  and the screw mechanism  253  abut on the stopper  258 , the lens holder  252  and the screw mechanism  253  stop at a position as abutting on the stopper  258 , however, the rotation shaft  255   b  receives a reaction force from the stopper  258  and starts to move in a reverse direction. The rotation shaft  255   b  moves till the rotation shaft  255   b  abuts on the first thrust bearing  255   d  or the second thrust bearing  256 , after that, the rotation shaft  255   b  cannot move due to loss of synchronism of the motor  255  and stops. 
         [0028]    Conventionally, the second thrust bearing  256  mounted at the shaft end on the output side of the rotation shaft  255   b  has not been provided with a position adjustment function, and an amount of movement to the output shaft end side of the rotation shaft  255   b  has not been controlled. Therefore, there has been a case where the motor rotor had abutted on the side surface in the motor case  255   a  and had stopped before the rotation shaft  255   b  has abutted on the second thrust bearing  256 . As described above, when the motor rotor stops due to the contact in the motor, there arises a drawback that escapement in the reverse direction cannot be made because of a large contact resistance. Consequently, in the present first embodiment, a position adjustment function with respect to the thrust direction is provided at the second thrust bearing  256  which is provided at the shaft end on the output side of the rotation shaft  255   b,  and the position in the thrust direction of the second thrust bearing  256  is adjusted so as to abut on the second thrust bearing  256  before contact is made in the motor. 
         [0029]    Next, a method of manufacturing the spherical aberration correction means  25  of the optical pickup  2  according to the first embodiment of the present invention will be described. 
         [0030]    First, the motor  255  is mounted to the base  257   a.  Next, the screw mechanism  253  is engaged with the lead screw  255   c  of the motor  255 . Engagement of the screw mechanism  253  can be implemented by rotating and pulling in the rotation shaft  255   b . As for the rotation of the rotation shaft  255   b,  there are methods in which a current is flown through the motor  255  to drive and in which a groove fitting to the driver  259   a  is provided at the tip end of the rotation shaft  255   b  to rotate by the driver  259   a.  Next, the lens holder  252  is loaded with so as to abut on the screw mechanism  253 , and the base  257   b  is fixed to the base  257   a  while exerting preload by the preload means  254 . Since an aperture with which the second thrust bearing  256  is engaged is provided in the base  257   b,  the driver  259   a  is inserted through the aperture to rotate the rotation shaft  255   b , and a position of the lens holder  252  can be readjusted. Next, the second thrust bearing  256  is mounted on the aperture provided in the base  257   b  using the assembly jig  259 . The second thrust bearing  256  is assembled while adjusting an amount of movement of the rotation shaft  255   b  in the thrust direction. First, the second thrust bearing  256  is fastened in a direction of the motor case  255   a  by rotating the driver  259   a . At this time, the electrical continuity checker  259   b  is provided between the driver  259   a  and the probe  259   c  abutted on the first thrust bearing  255   d,  and the fastening operation is performed till electrical continuity is confirmed by the electrical continuity checker  259   b.  After confirming the electrical continuity, the driver  259   a  is reversely rotated for a predetermined angle to loosen the second thrust bearing  256 . After that, adhesive is applied to the second thrust bearing  256  by the bonding instrument  259   d,  to fix to the base  257   b.  As described above, the spherical aberration correction means  25  is manufactured, and accordingly, adjustment operation of the amount of movement of the rotation shaft  255   b  in the thrust direction can be efficiently implemented. 
         [0031]    As described above, according to the present first embodiment, the amount of movement of the rotation shaft  255   b  in the thrust direction can be accurately controlled by the second thrust bearing  256 . With this, when the lens holder  252  and the screw mechanism  253 , which are stopped by abutting on the stopper  258 , are driven in the reverse direction, operation can be surely performed. In addition, the adjustment operation of the second thrust bearing  256  can be easily implemented by the assembly jig  259  using the electrical continuity checker  259   b,  and therefore, operating efficiency is good and productivity is high. With these features, an optical pickup with high reliability and high productivity can be provided. 
       Second Embodiment  
       [0032]    An optical pickup according to a second embodiment of the present invention will be described with reference to  FIG. 4 . 
         [0033]      FIG. 4  shows a configuration and a manufacturing method of spherical aberration correction means  25  mounted on an optical pickup  2  according to the second embodiment of the present invention. 
         [0034]    In  FIG. 4 , reference numeral  259   e  denotes a spacer and other configuration is the same as  FIG. 3 . 
         [0035]    In the present second embodiment of the present invention, an aperture which is for attaching and detaching a spacer is provided on a base  257   b.  The aperture is provided in a radial direction between a rotation shaft  255   b  and a first thrust bearing  255   d,  or between the rotation shaft  255   b  and a second thrust bearing  256 .  FIG. 4  shows a structure in which the aperture is provided on the second thrust bearing  256  side. The spacer  259   e  is a metal piece having a predetermined thickness and is sandwiched between the rotation shaft  255   b  and the second thrust bearing  256 , and accordingly, a distance between the two is correctly controlled. 
         [0036]    A method of manufacturing spherical aberration correction means  25  of an optical pickup  2  according to the second embodiment of the present invention will be described. 
         [0037]    First, a motor  255  is mounted to a base  257   a.  Next, a screw mechanism  253  is engaged with a lead screw  255   c  of the motor  255 . Engagement of the screw mechanism  253  can be implemented by rotating and pulling in the rotation shaft  255   b . Next, a lens holder  252  is loaded with so as to abut on the screw mechanism  253 , and the base  257   b  is fixed to the base  257   a  while exerting preload by preload means  254 . Next, the spacer  259   e  is inserted through the aperture for attaching and detaching the spacer provided in the base  257   b  and is sandwiched between the rotation shaft  255   b  and the second thrust bearing  256 . Next, the second thrust bearing  256  is mounted on the aperture provided in the base  257   b  using an assembly jig  259 . The second thrust bearing  256  is assembled while adjusting an amount of movement of the rotation shaft  255   b  in a thrust direction. First, the second thrust bearing  256  is fastened in a direction of the motor case  255   a  by rotating the driver  259   a.  At this time, an electrical continuity checker  259   b  is provided between the driver  259   a  and a probe  259   c  abutted on the first thrust bearing  255   d,  and the fastening operation is performed till electrical continuity is confirmed by the electrical continuity checker  259   b.  After confirming the electrical continuity, removal operation of the spacer  259   e  is performed. After that, adhesive is applied to the second thrust bearing  256  by a bonding instrument  259   d,  to fix to the base  257   b.  As described above, the spherical aberration correction means  25  is manufactured, and accordingly, adjustment operation of the amount of movement of the rotation shaft  255   b  in the thrust direction can be efficiently implemented. 
         [0038]    As described above, according to the present second embodiment, the amount of movement of the rotation shaft  255   b  in the thrust direction can be accurately controlled by the spacer  259   e.  With this, the adjustment operation of the second thrust bearing  256  can be easily implemented, and therefore, operating efficiency is good and productivity is high. With these features, an optical pickup with high productivity can be provided.