Abstract:
There is disclosed a lens holder capable of firmly holding the objective lens of an optical pickup to the holder without contamination of the effective range of the objective lens due to adhesive. An optical pickup using this lens holder is also disclosed. The lens holder  10  has a seat portion  3  for locking the objective lens  1  of the optical pickup. The seat portion  3  has a top-end surface  3   a  that is inclined and sinks outward.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to optical pickups for reading and writing information to and from an optical recording medium, such as an optical disk, and to lens holders used in such an optical pickup. 
     2. Description of the Related Art 
     Generally, an optical pickup of this kind has a laser light source for emitting a laser beam and optics for guiding the emitted laser beam to a recording medium such as an optical disk. A rewritable recording medium, such as CD-Recordable or CD-Rewritable, permits reading of information, as well as writing of information. With an optical pickup for CD-Recordable, it is necessary to switch the output level of the laser beam emitted from a laser light source, depending on whether information is read or written, for the following reason. To write information, laser beam is radiated to form pits in the recording layer of an optical disk. The output of the laser beam is emitted from the laser light source during writing of information and is higher than the output emitted during reading of information. For example, the former output is about 10 to 20 times as large as the latter output. 
     An optical pickup used for an optical disk drive, such as a CD recorder, comprises an optical base, a lens holder, a damper base connected to the lens holder via suspension wires, and an actuator base that accommodates both lens holder and damper base. The lens holder is equipped with an objective lens, a tracking coil, and a focusing coil. The actuator is formed integrally with a yoke having a magnet for driving the lens holder by making use of the interaction between the tracking coil and the focusing coil. 
     The optical pickup has a laser acting as a light source that emits a laser beam. The laser beam emitted from the laser is made to hit an optical disk, such as a CD-R disk, that is an optical recording medium through a diffraction grating, a beam splitter, a collimator lens, and an objective lens. Light reflected from the optical disk impinges on a photodiode (PD) that is a light-receiving device through the objective lens, the collimator lens, and the beam splitter. That is, the photodiode receives the light reflected from the optical disk. Optical parts include the laser and the beam splitter and are held to the optical base. 
     The lens holder of the objective lens has flat support portions, a seat portion cylindrically protruding from parts of the flat supports, and the aforementioned objective lens installed on the seat portion. The seat portion is provided with crisscross grooves extending diametrically. Claws protrude upward from the grooves. 
     The optical lens of the optical pickup and the lens holder for holding the pickup are bonded together by placing the objective lens on the flat top-end surface of the seat portion of the lens holder and using an adhesive, such as a UV-curable resin. 
     If the flat top-end surface of the seat portion on which the objective lens is to be placed is partially concave, the adhesive may soak through the objective lens toward its center. If this adhesive reaches a portion of the objective lens through which light can pass (hereinafter referred to as the effective region of the objective lens), the optical characteristics of the pickup will deteriorate. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a lens holder capable of firmly holding the objective lens of an optical pickup to the holder via an adhesive without contamination of the effective range of the objective lens due to the adhesive. 
     It is another object of the invention to provide an optical pickup for use in the lens holder described in the immediately preceding paragraph. 
     According to one aspect of the present invention, there is provided an optical pick up which has a lens holder on which an objective lens is held, an actuator base, a damper base connected to the actuator base, and suspension wires. The lens holder has a seat portion for locking said objective lens. The seat portion has a top-end surface. 
     In the aspect of the present invention, an inclined surface is formed in said top-end surface of said seat portion and sinking outward. 
     According to another aspect of the present invention, there is provides a lens holder which has a seat portion for locking an objective lens of an optical pick up. The seat portion has a top-end surface that is an inclined surface sinking outward. 
     Other objects and features of the invention will appear in the course of the description thereof, which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of an optical pickup in the Prior Art; 
     FIG. 2A is a plan view of a lens holder shown in FIG. 1; 
     FIG. 2B is a front elevation view of the lens holder shown in FIG. 2A, but in which the lens has been removed; 
     FIG. 2C is a fragmentary enlarged cross sectional view of the bonded surface of a lens shown in FIG. 2A; 
     FIG. 3 is a partially plan view illustrating the state of adhesive applied to the prior art lens holder; 
     FIG. 4 is a fragmentary enlarged cross sectional view of the adhesively bonded portion of the prior art lens holder; 
     FIG. 5 is a rear view of main portions of an optical pickup in accordance with an embodiment of the invention; 
     FIG. 6A is a plan view of a lens holder shown in FIG. 5; 
     FIG. 6B is a side elevation view of the optical pick up shown in FIG. 5, but in which the lens holder has been removed; 
     FIG. 6C is a fragmentary enlarged cross section of a bonded portion of a lens shown in FIG. 6A; 
     FIG. 7 is a fragmentary cross sectional view illustrating the action of the lens holder shown in FIG. 6A; and 
     FIG. 8 is a fragmentary plan view illustrating the action of the lens holder shown in FIG.  6 A. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before describing the preferred embodiments of the present invention, a conventional pickup is described by referring to FIGS. 1-4 to better understand the invention. 
     Referring to FIG. 1, an optical pickup  11  is used in an optical disk drive, such as a CD recorder. The pickup  11  includes an optical base  13 , a lens holder  17 , a damper base  19 , and an actuator base  21 . The lens holder  17  is equipped with an objective lens  15 , a tracking coil (not shown), and a focusing coil (not shown). The actuator base  21  houses the lens holder  17  and the damper base  19 . 
     The optical pickup  11  has a laser  23  acting as a light source for radiating a laser beam. The laser beam emitted from the laser  23  is directed onto an optical disk (CD-R) disk that is an optical recording medium through a diffraction grating, a beam splitter, and a collimator lens (none of which are shown) and through the objective lens  15 . Light reflected from the optical disk hits a photodiode (not shown) that is a light-receiving device through the objective lens  15 , the collimator lens, and the beam splitter. That is, the photodiode receives the light reflected from the optical disk. 
     Optical parts including the laser  23  and the beam splitter are held to the optical base  13 , which in turn is securely mounted to the enclosure (not shown) of the optical disk drive. A printed-circuit board  25  is mounted to a side surface of the optical base  13 . The printed-circuit board  25  is electrically connected with other electrical parts (not shown) of the optical disk drive via a flexible cable  27  connected with the board  25 . 
     The lens holder  17  and the damper base  19  are connected together by plural suspension wires  29 , thus forming a subassembly accommodated in the actuator base  21 . A part of the actuator base  21  forms a yoke  31  with which a magnet is combined. 
     The actuator base  21  comprises a frame molded from a metallic material and has a damper base-receiving portion (not shown) at a side of one end of the frame to receive the damper base  19 . A support block  33  for locking the damper base  19  is present in this receiving portion. The support block  33  is molded integrally with the actuator base  21 . Substantially semicircular protrusions  37  are formed on both sidewalls of the frame and are held by support portions  35  formed on the optical base  13 . 
     A damper base cover  39  is molded from a transparent resinous material and is mounted to the damper base  19 , and has also a rear portion on which fixing portions  41  for anchoring respective one end of the suspension wires  29  are mounted. A vibration-damping material (not shown) is injected in the space between the damper base  19  and the damper base cover  39  to damp vibrations of the suspension wires  29 . 
     A flexible circuit  43  to be soldered to ends of the suspension wires  29  that are located ahead of the fixed ends is mounted on the rear wall of the damper base  19 . The damper base  19  is inserted in the space among the sidewalls of the actuator base  21  and the support block  33  and made stationary. 
     The support block  33  and the damper base  19  are squeezed in between a screw (bolt)  45  and a nut  47 . The damper base  19  is rotatable about the screw to permit adjustment of the skew. 
     Before the damper base  19  is fixedly mounted to the actuator base  21 , the suspension wires  29  are mounted to the damper base  19 . That is, the lens holder  17  and the damper base  19  are assembled into a unit by the plural suspension wires  29 . The resulting unit is received and mounted in the actuator base  21 . 
     Referring to FIGS. 2A,  2 B, and  2 C, the lens holder  17  of the objective lens has flat support portions  49 ,  51 , a seat portion  53  cylindrically protruding from the support portion  49 , and the aforementioned objective lens  15  installed on the seat portion  53 . The seat portion  53  is provided with crisscross grooves  55  extending diametrically. Claws  57  protrude upward from the grooves  55 . 
     The objective lens  15  of the optical pickup and the lens holder  17  holding the pickup are fastened together by placing the objective lens  15  on a flat top-end surface  59  of the seat portion  53  of the lens holder  17  and using an adhesive such as a UV-curable resin, as best shown in FIG.  2 C. The bottom end surface of the fringing portion of the objective lens, the outer side surface, and the top end surface of the fringing portion of the objective lens are indicated by  65 ,  67 , and  69 , respectively. 
     Referring next to FIGS. 3 and 4, if a gap or recess is present in a part of the flat top-end surface  59  of the seat portion  53  on which the objective lens  15  is placed, adhesive  63  may soak through the objective lens  15  toward its center as indicated by an arrow  61  in FIG.  4 . If this adhesive reaches a portion of the objective lens  52  through which light can pass, (hereinafter referred to as the effective region of the objective lens) the optical characteristics of the pickup will deteriorate. 
     Now description will be made as regards the preferred embodiment of the present invention with reference to FIGS. 5-8. 
     Referring to FIG. 5, an optical pickup is equipped with a lens holder  71 , an actuator base  73 , a damper base  75  connected to the actuator base  73 , and suspension wires  77 . An objective lens  15  is mounted on the lens holder  71 . 
     Referring next to FIGS. 6A and 6B, the lens holder  71  has a support portion  79  at one end. A seat portion  81  protrudes cylindrically from the support portion  79 . The seat portion  81  is formed with crisscross grooves  83  extending diametrically. Claws  85  protrude upward from the top ends of the grooves  83 , and are used to place and lock the objective lens in position. 
     As best shown in FIG. 6C, the seat portion  81  has a top-end surface  87  on which the periphery of the objective lens  15  is placed. This top-end surface  87  is inclined mildly outwardly. 
     The action and advantages of this lens holder  71  in accordance with one embodiment of the invention are next described by referring to FIGS. 7 and 8. 
     Referring to FIG. 7, a surface of the objective lens  15  used for adhesive bonding normally consists of the top-end surface  87  of the seat portion  81  of the lens holder  71  and the outer surface  67  of the objective lens  15 . A slight gap is created between the bottom surface  65  of the peripheral portion of the objective lens  15  and the inclined top-end surface  87 , whereby the bottom surface acts as an adhesive surface. By tilting the top-end surface  87  of the seat portion  81 , an extra portion of adhesive  89  flows along the downwardly inclined surface of the top-end surface  87  toward the outer periphery of the objective lens  15  as indicated by an arrow  91  without leaking toward the center of the objective lens  15 . 
     In the lens holder  71  of the construction as described above, the applied adhesive  89  spreads over the whole gap between the objective lens  15  and the seat portion  81  of the lens holder  71  by capillarity as indicated by the arrow  93  in FIG.  8 . Consequently, the adhesive  89  permeates the whole outer surface of the objective lens, thus enhancing the adhesion. As a result, stronger surface adhesion is possible. 
     As described thus far, the present invention prevents extra adhesive  89  on the seat portion  81  of the objective lens  15  of the lens holder  71  from leaking toward the center of the objective lens  15 ; otherwise, the effective range of the objective lens  15  would be contaminated. Furthermore, the adhesive  89  permeates uniformly the gap between the objective lens  15  and the lens holder  71 . Hence, the lens holder  71  capable of stronger adhesive bonding and an optical pick up using this lens holder can be provided.