Abstract:
There is provided an optical pickup for use in an information reproducing apparatus for playing an optical disc, said optical pickup comprising: a main pickup body carrying an objective lens; a sub-pickup body pivotably connected with the main pickup body; a connecting structure formed in connection with the main pickup body for pivotably supporting the sub pickup body. A space having a predetermined size is formed between the main pickup body and the connecting structure. The material thickness between the main pickup body and the connecting structure is made thinner by virtue of the formation of said groove.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an optical pickup which is indispensable part for an information reproducing apparatus (disc player) for playing a CD (compact disc) and a DVD (digital video disc). 
     A compact disc (hereinafter referred to as CD) comprises a plastic layer (having a thickness of 1.2 mm) on which audio or video signals are recorded in the form of numerous information pits, a metal reflecting layer formed on the plastic layer, and a protection layer formed on the reflecting layer. 
     A digital video disc (hereinafter referred to as DVD) comprises two information layers on each of which signals are recorded in the form of numerous information pits, each having a thickness of 0.6 mm. Such a DVD is capable of recording a much larger amount of information than a CD. 
     Although a CD and a DVD are different from each other in their specifications, a CD drive of a CD player has many similarities with a DVD drive of a DVD player. Thus, there has been suggested an optical disc player which has two optical pickups adapted to play a CD and a DVD, using only a single disc drive. 
     However, in the optical disc player designed to play a CD and a DVD, since there are two optical pickups, two sets of moving mechanisms are required to respectively move the two optical pickups in disc radial direction. As a result, it is difficult for a disc player to be made compact. 
     In view of the above, a more compact player has been demanded which has only a single optical pickup capable of playing not only a CD but also a DVD. For instance, the single optical pickup is made into two-focus pickup capable of emitting an optical beam for playing both a CD and a DVD (whose protection layers are different from each other in thickness). However, in a case where a two-focus optical pickup is employed in a disc player, if there is an inclining angle between the recording surface of an optical disc and the optical axis of the optical beam, a comatic aberration will occur in the optical beam when irradiating an optical disc. in order to correct such a comatic aberration, a pickup including an actuator is moved in disc radial direction or disc tangential direction, thereby eliminating the inclining angle between the recording surface of an optical disc and the optical axis of an optical beam. 
     On the other hand, since an optical beam for DVD and an optical beam for CD are caused to pass through an identical objective lens with different incident angles, an attempt to eliminate a comatic aberration occurring in one optical beam will undesirably promote a comatic aberration occurring in the other optical beam. Namely, it is difficult to eliminate two kinds of comatic aberration occurring in two optical beams. 
     In order to solve the above problem, at first the pickup body is caused to incline to some extent to eliminate a comatic aberration occurring in one optical beam. Then, the actuator of the pickup body is caused to incline to some extent in a direction in which a comatic aberration occurs in the other optical beam. Further, it is also possible to have the pickup body inclined to at the same time eliminate the above two kinds of comatic aberration occurring in the above two optical beams. 
     It is understood from the above explanation that, in order to correct two kinds of comatic aberration occurring in two optical beams, it is necessary to establish a construction where the pickup body of the two-focus pickup may be made inclined with respect to the recording surface of an optical disc. For instance, it is required that the pickup body be divided into a main pickup body and a sub-pickup body, both of which are pivotably connected with each other, such that the main pickup body may be made inclined so as to correct the above comatic aberration. 
     However, in a construction where the main pickup body and a sub-pickup body are pivotably connected with each other, a resonance phenomenon will occur in both the main pickup body and the sub-pickup body due to a vibration from the outside, resulting in a problem that information can only be reproduced with a deteriorated precision. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved optical pickup capable of reproducing information from an optical disc with a high precision even if there is a vibration from the outside, so as to solve the above-mentioned problems peculiar to the above-mentioned prior arts. 
     According to the present invention, there is provided an optical pickup for use in an information reproducing apparatus for playing an optical disc, said optical pickup comprising: a main pickup body carrying an objective lens; a sub-pickup body pivotably connected with the main pickup body; a connecting structure formed in connection with the main pickup body for pivotably supporting the sub-pickup body. A groove having a predetermined size is formed between the main pickup body and the connecting structure. The material thickness between the main pickup body and the connecting structure is made thinner by virtue of the formation of said groove. 
     In detail, the above connecting structure is connected to the sub-pickup body through a support portion of the sub pickup body. The support portion of the sub-pickup body is formed with a screw hole into which a screw is engaged. Similarly, the connecting structure is also formed with a screw hole. Thus, a screw engaged in the screw hole of the support portion of the sub-pickup body is engaged into the screw hole of the connecting structure. 
     The above objects and features of the present invention will become more understood from the following description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a top plane view showing one embodiment of an optical pickup according to the present invention. 
     FIG. 2 is a bottom plane view of the optical pickup of FIG.  1 . 
     FIG. 3 is a cross sectional view showing a grating holder used in the optical pickup of FIG.  1 . 
     FIG. 4 is a front view showing the grating holder of the FIG.  3 . 
     FIG. 5 is a cross sectional view showing the optical axis of the grating holder of FIG.  3 . 
     FIG. 6 is a front view showing a multi-lens holder of the optical pickup of FIG.  2 . 
     FIG. 7 is a top plane view showing the multi-lens holder of FIG.  6 . 
     FIG. 8 is an explanatory view showing how to adjust the position of the multi-lens holder of FIG.  6 . 
     FIG. 9 is a cross sectional view showing a main pickup body of the optical pickup of FIG.  1 . 
     FIG. 10 is an explanatory view showing how terminals of a connector are connected to a print substrate. 
     FIG. 11 is a cross sectional view showing how a coil-like spring is used to support a grating holder. 
     FIG. 12 is a cross sectional view showing how a coil-like spring is used to support a grating holder. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2, an optical pickup of the present invention includes a main pickup body  100  and a sub pickup body  200 . On the side face (on the right side in FIGS. 1 and 2) of the sub-pickup body  200 , there is provided a rack (not shown) arranged in a vertical direction as viewed in FIGS. 1 and 2. A driving pinion (not shown) is engaged with said rack. 
     On the other hand, the pickup body  100  has a support portion  100   a  on which a rod (not shown) is provided in parallel with the above rack. In detail, an urging member having a predetermined elasticity is provided on the underside of the support portion  100   a , the above rod is supported on the urging member. Further, a screw hole is formed through the support portion  100   a , and an adjusting screw (not shown) is engaged in the said screw hole, such that a frond end of the screw is in contact with the above rod. In this way, the rod may be firmly pressed between the above urging member and the front end of the above adjusting screw. When the main pickup body  100  is moved in a direction that is the rod axis direction, the above urging member and the front end of the above adjusting screw will slid in contact with the above rod, thus the movement of the main pickup body  100  will not be hampered. In this way, the pickup body  100  may be freely moved in the rod axis direction (disc radial direction) by rotating the above driving pinion. 
     As shown in FIG. 2, a laser diode  110  for emitting an optical beam is mounted in a notch  101  of the main pickup body  100 . An optical beam from the laser diode  110  is adjusted in its optical axis by virtue of a grating element  124  (FIG. 3) held on a grating holder  120  which has an optical axis adjusting member  121 . The grating holder  120  is attached in another notch  102  which is communicated with the notch  101 . 
     Referring to FIGS. 3 and 4, the grating holder  120  is formed with a hollow portion  122 . A glass plate  123  is provided at one end of the hollow portion  122 , a grating element  124  is provided at the other end of the hollow portion  122 . The optical beam from the laser diode  110  is received through the glass plate  123  and emitted through the grating element  124 . 
     Further, as shown in FIG. 2, the grating holder  120  is urged in the optical axis direction towards the laser diode  110  by virtue of a coil-like spring  125  (FIG.  1 ). As shown in FIG. 1, since one end  125   b  of the coil-like spring  125  is urged by an elastic member  126  towards the main pickup body  100 , the other end  125   a  of the coil-like spring  125  will also be urged towards to the main pickup body  100 . In this way, the optical axis adjusting member  121  of the grating holder  120  in tight contact with the end  125   a  will also be urged towards the main pickup body  100 . As a result, by virtue of the coil-like spring  125 , the grating holder  120  will be urged at the same time towards both the laser diode  110  and the main pickup body  100 . 
     Referring to FIG. 5, with the use of the above-described construction, when the optical axis of an optical beam from the laser diode  110  is to be adjusted, an adjusting screw  127  screwed upwardly through the main pickup body  100  may be slightly screwed up or down. In this manner, by turning the grating holder  120  using the optical axis adjusting member  121 , the diffraction pattern of the grating element  124  may be made inclined so that the diffracting direction is changed. At this moment, the grating holder  120  may be fixed in the inner space  102 , by virtue of the upward force of the adjusting screw  127  and the elastic force of the coil-like spring  125 . 
     The optical beam passing through the grating holder  120  is bent at a reflecting mirror  130  (mounted in a notch  103 ) for 90°, so as to arrive at a prism  140  (mounted in the same notch  103 ), as shown in FIG.  2 . 
     Further, the optical beam passing through the prism  140  becomes parallel beam upon passing through a collimator lens  150 . Then, the parallel beam is bent for another 90° by means of another reflecting mirror (not shown) so as to pass through an objective lens (not shown) provided in a hole  104 . Finally, the optical beam passing through the objective lens is converged onto a recording surface of an optical disc. 
     The returning beam from the recording surface of the optical disc is directed backwardly by way of the objective lens (not shown), the collimator lens  150 , the reflecting mirror (not shown) and the prism  140 . Then, the returning beam is directed to a photo-detector  170  (FIG. 2) by way of a multi-lens  160 A (FIGS. 6 and 7) held by a multi-lens holder  160  (attached in a notch  105  which is communicated with the notch  103 .) 
     Referring again to FIG. 2, the multi-lens holder  160  is elastically held in the notch  105  by virtue of a support portion  181  of an elastic support member  180  (which is secured on the main pickup body  100 ). Further, a hemispherical projection  182  formed on the support portion  181  of the elastic support member  180  is embeded in a notch  163  of the multi-lens holder  160 . 
     The multi-lens  160 A held by the multi-lens holder  160  has a function of cylindrical lens causing astigmatic aberration, and a function of convex lens collecting returning beam from the optical disc onto the photo-detector  170 . 
     Further, as shown in FIGS. 6 and 7, the multi-lens holder  160  has support portions  162 ,  162  extending in the horizontal direction, and a main body portion  161  formed between the support portions  162 ,  162 . When the multi-lens holder  160  is attached in the notch  105  of the main pickup body  100 , the support portions  162 ,  162  become in contact with support projections  107 ,  107  of the notch  105 , so that the multi-lens holder  160  may be arranged in a predetermined position in the main pickup body  100 . In such an arrangement, the body portion  161  of the multi-lens holder  160  will avoid getting contact with the inner wall of the notch  105 . 
     An optimum position of the multi-lens  160 A held by the multi-lens holder  160 , i.e., a position that allows the photo-detector  170  to obtain a desired amount of reflecting beam, may be adjusted by an adjusting jig  220  (FIG. 8) of an automatic adjusting mechanism. 
     Referring to FIG. 8, the adjusting jig  220  of the automatic adjusting mechanism is caused to engage on the upper portion of the multi-lens holder  160 , making the multi-lens holder  160  to have a tendency to move in the optical axis direction. At this moment, an acting point of the adjusting jig  220  on the multi-lens holder  160  will be close to the contact surfaces between the support portions ( 162 ,  162 ) and the support projections ( 107 ,  107 ). In this way, even if the adjusting jig  220  has its acting force collected at one point on the upper portion of the multi-lens holder  160 , the contact faces between the support portions ( 162 ,  162 ) and the support projections ( 107 ,  107 ) will serve to prevent the multi-lens  160 A from falling down in the moving direction of the multilens holder  160 , ensuring a smooth movement of the multi-lens holder  160 . Therefore, it becomes possible to adjust the multi-lens  160 A to its optimum position with a high precision. 
     As shown in FIG. 6, since the multi-lens holder  160  is urged only by a projection  182  of a support member  181 , the multi-lens holder  160  may be freely turned to some extent with the projection  182  as a turning center. 
     Referring again to FIGS. 1 and 2, since the screw  210  engaged in the screw hole  202  of the support portion  201  of the sub-pickup body  200  is engaged into a screw hole of a connecting structure  183  formed in connection with the main pickup body  100 , the main pickup body  100  and the sub-pickup body  200  are connected to be relatively pivotable with respect to each other. Thus, it is seen that the connecting structure  183  is connected to the sub-pickup body  200  through its support portion  201 . After the comatic aberration in the two-focus optical pickup has been corrected, the screw  210  may be further fastened, so that the main pickup body  100  and the sub-pickup body  200  may be fixed together. 
     Further, between the connecting structure  183  and the main pickup body  100  there is formed a groove  184  having a predetermined size and depth. As shown in FIG. 9, due to the formation of the groove  184 , the material thickness between the main pickup body  100  and the connecting structure  183  may be made thinner, thereby prohibiting or at least reducing a resonance phenomenon between the main pickup body  100  and the sub-pickup body  200  by reducing a vibration transmitting between the two. 
     Namely, in the optical pickup of the present invention, the rigidity of the connecting structure  183  (for connecting the main pickup body  100  with the sub-pickup body  200 ) will vary wit h the depth and length of the groove  184 . In fact, the resonant frequency of the sub-pickup body  200 , which depends upon the mass of the sub-pickup body  200  and the rigidity of the connecting structure  183 , may be utilized to determine the shape of the groove  184 , such that the resonant frequency of the sub-pickup body  200  will be different from the resonant frequency of the main pickup body  100 . 
     Referring again to FIG. 1, a connector  190  is attached to an attachment section  108  of the main pickup body  100 . 
     In the present embodiment, as shown in FIG. 10, a plurality of terminals  191  formed on the connector  191 , are connected by means of solderring to a print substrate  230  provided on the attachment section  108 . The print substrate  230  is formed by spreading a layer of copper foil  232  over a base layer  231 , followed by bonding a cover layer  233  over the copper foil  232 . The cover layer  233  is formed with a plurality of holes  234  which permit the terminals  191  to be embeded into the print substrate  230 . Further, a plating layer (not shown) is formed on the copper foil  232  over the areas corresponding to the holes  234 . 
     The main body  190 A of the connector  190  is attached on the cover layer  233 , so that each terminal  191  is in con tact with the copper foil  232  through the plating layer (not shown). 
     In this way, all the terminals  191  may be attached to the copper foil  232 , facilitating the positioning of the connector  190  onto the print substrate  230 . Finally, solderring is performed to permanently connect the terminals  191  to the print substrate  230 . The above arrangement of the terminals  191  on the print substrate  230  not only allows an easy solderring operation, but also prevents a problem of solderring bridge occurring between two terminals  191  (even if a pitch of every two terminals is small). 
     The operation of the optical pickup having a construction as described above will be described in more detail as follows, with reference to FIGS. 1 and 2. 
     At first, when information recorded on an optical disc is to be reproduced, the pinion engaging with the rack provided on the sub-pickup body  200  is driven so as to apply a driving force to the pickup body  200 . At this moment, the main pickup body  100  is guided by the rod (not shown), the support member  204  of the sub-pickup body  200  is guided by a guide shaft (not shown), so that the optical pickup  10  is caused to move in the radial direction of the optical disc. 
     Then, an optical beam is emitted from the laser diode  110 . The optical beam is at first diffracted by the grating element  124  held on the grating holder  120 , and is bent at the reflecting mirror  130  for 90° so to arrive at the prism  140 . 
     Further, the optical beam passing through the prism  140  becomes parallel beam through a collimator lens  150 . Then, the parallel beam is bent for another 90° by means of another reflecting mirror (not shown) so as to pass through an objective lens (not shown) provided in a hole  104 . Finally, the optical beam passing through the objective lens is converged onto the recording surface of an optical disc. 
     The returning beam from the recording surface of the optical disc is directed backwardly by way of the objective lens (not shown), the collimator lens  150 , the reflecting mirror (not shown) and the prism  140 . Then, the returning beam is directed to a photo-detector  170  (FIG. 2) through the multi-lens  160 A (FIG. 7) held by a multi-lens holder  160  (attached in a notch  105  communicated with the notch  103 .) 
     During the above operation, since there is formed a space  184  between the connecting structure  183  and the main pickup body  100 , if there is a vibration from outside, it is possible to prohibit a resonance phenomenon between the main pickup body  100  and the sub-pickup body  200  by reducing a vibration transmitting therebetween, thereby enabling a stabilized information reproduction. 
     In the embodiment shown in FIGS. 1 and 2, the grating holder  120  is urged by the coil-like spring  125  towards the laser diode  110 . Thus, effected by the coil-like spring  125 , the grating holder  120  receives not only an urging force to push the grating holder  120  towards the laser diode  110 , but also an urging force to cause the grating holder  120  to turn about the optical axis of the grating element  124 . There is a possibility that the coil-like spring  125  will deform to some extent due to an upward force produced by the adjusting screw  127 . The deformation of the coil-like spring  125  will cause the grating holder  120  to incline a little, resulting in a deviation of optical axis from its correct position. In order to avoid this problem, as shown in FIG. 11, a holding member  125   a  for holding the grating element  124  is made to have a smaller diameter portion, thus reducing a direct contact between a coil-like spring  125 A and the holding member  125   a.    
     In this manner, as shown in FIG. 11, the middle portion of the coil-like spring  125 A will not get contact with the holding member  125   a . Thus, even if the coil-like spring  125 A is deformed to some extent due to an upward force produced by the adjusting screw  127 , the deformation of the coil-like spring  125 A will not cause the grating holder  120  to incline, thereby avoiding a deviation of optical axis. In addition, since the middle portion of the coil-like spring  125 A does not get contact with the grating holder  120 , it becomes possible for the grating holder  120  to avoid a resonant phenomenon caused due to an outside vibration. Further, as shown in FIG. 11, if an annular space  101   b  for the coil-like spring  125 A to escape is formed in the main pickup body  100 , even better effect will be obtained. 
     Moreover, as shown in FIG. 12, a coil-like tapered spring  125 B may be used in the optical pickup, with its larger diameter portion  125   d  held at an annular recess  101   a  formed in the main pickup body  100 , and its smaller diameter portion  125   c  engaged on the grating holder  120 . 
     In an embodiment shown in FIG. 12, the grating holder  120  is urged by the coil-like spring  125 B towards the laser diode  110 . Thus, effected by the coil-like spring  125 B, the grating holder  120  receives not only an urging force to push the grating holder  120  towards the laser diode  110 , but also an urging force to cause the grating holder  120  to turn about the optical axis of the grating element  124 . At this time, even if the coil-like spring  125  is deformed to some extent due to an upward force produced by the adjusting screw  127 , since only the smaller diameter portion  125   c  of the coil-like tapered spring  125 B will engage on the grating holder  120 , the deformation of the coil-like spring  125 B will not cause the grating holder  120  to incline, thereby avoiding a deviation of optical axis. In addition, since the coil-like spring  125 B can exert a considerable pressing force on the grating holder  120 , it becomes possible for the grating holder  120  to avoid a resonance phenomenon caused due to an outside vibration. 
     While the presently preferred embodiments of the this invention have been shown and described above, it is to be understood that these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.