Abstract:
In an optical pickup projecting a laser beam from a laser diode onto a disk through a half mirror, a collimator lens and an objective lens and receiving the laser beam reflected by the disk in a photodiode through the half mirror thereby reading information recorded in the disk, a portion of a metal board body having a pattern of a printed board corresponding to a connector pin fed with a high-frequency signal is notched to cause no electrostatic capacitance between the metal board body and the printed board thereby preventing a read signal from the photodiode from a jitter. Thus obtained is a high-performance and low-priced optical pickup causing no reading error.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an optical pickup, and more particularly, it relates to a high-performance and low-priced optical pickup, employed for a disk player such as a DVD, for example, causing no reading error. 
   2. Description of the Background Art 
   For example, Japanese Patent Laying-Open No. 8-7321 describes an optical pickup.  FIG. 8  is a schematic sectional view showing an example of such a conventional optical pickup. Referring to  FIG. 8 , a photodiode PD is arranged in an opening  3   a  formed on an end of a light transmission hole  3  provided with a half mirror  2  in a pickup body  1 , while a collimator lens CL and an objective lens OL are arranged in another opening  3   b  formed on another end of the light transmission hole  3 . A laser diode LD is stored in a branch hole  4  formed on a side surface of the pickup body  1 . A printed board  6  connected with the photodiode PD and the laser diode LD through flexible cables  5  is fixed to the outer peripheral surface of the pickup body  1  with a machine screw  7 . 
   A support substrate  8  supports the laser diode LD. A plug-in unit  10  is connected to a connector  9  fixed to the printed board  6  thereby connecting the photodiode PD and the laser diode LD to a control part (not shown) such as a microcomputer. 
   In the optical pickup shown in  FIG. 8 , the laser diode LD projects a laser beam onto a disk D through the half mirror  2 , the collimator lens CL and the objective lens OL and the photodiode PD receives the laser beam reflected by the disk D through the half mirror  2  thereby reading information recorded in the disk D. 
   In this case, however, the laser diode LD disadvantageously generates heat due to the projection of the laser beam, and is reduced in capacity. In general, therefore, the pickup body  1  is molded by die-cast aluminum for prompting heat dissipation, while such a pickup body  1  of die-cast aluminum is high-priced. 
   Therefore, the pickup body  1  may be molded by low-priced hard synthetic resin while forming the support substrate  8  for the laser diode LD by a metal plate thereby prompting heat dissipation. 
   In the aforementioned structure, the metal support substrate  8  for the laser diode LD prompts heat dissipation. When the size of the support substrate  8  is increased for improving the heat dissipation effect, however, the bulked support substrate  8  comes into contact with a peripheral device. Therefore, the support substrate  8  is limited in size. When a high-performance laser diode LD is employed, further, the pickup body  1  is thermally expanded and deformed as shown by a phantom line in  FIG. 8  due to high calorific power of the laser diode LD, and an optical axis O connecting the photodiode PD and the objective lens OL may be bent to cause a reading error. Therefore, the laser diode LD must be formed by that having low calorific power, disadvantageously leading to a narrow selection range for the laser diode LD. 
   SUMMARY OF THE INVENTION 
   Accordingly, a principal object of the present invention is to provide a high-performance and low-priced optical pickup causing no reading error. 
   According to a first aspect of the present invention, the optical pickup has a photodiode arranged in an opening formed on an end of a light transmission hole provided with a half mirror in a pickup body of synthetic resin, a collimator lens and an objective lens arranged in an opening formed on another end of the light transmission hole and a laser diode stored in the light transmission hole on a position opposed to the half mirror. A printed board connecting the photodiode and the laser diode to a connector through cables is provided on the outer peripheral surface of the pickup body. Such structure as described above is aimed at projecting a laser beam from the laser diode onto a disk through the half mirror, the collimator lens and the objective lens and receiving the laser beam reflected by the disk in the photodiode through the half mirror, thereby reading information recorded in the disk. In this optical pickup, a board body of the printed board consists of a metal plate, and a metal plate portion of the printed board corresponding to a connector pin portion and a wiring pattern fed with a high-frequency signal is notched. An extension integrally provided on a metal support substrate for the laser diode is inserted in a concave groove formed on the outer peripheral surface of the pickup body for fixing the board body to the pickup body thereby bringing the board body into close contact with the extension and the outer peripheral surface of the pickup body. 
   In the metal plate forming the board body, the portion corresponding to the connector pin portion and the wiring pattern fed with the high-frequency signal is notched as hereinabove described, to cause no electrostatic capacitance between the metal plate and the printed board. Therefore, the high-frequency signal can be prevented from a jitter, not to influence a tracking signal. 
   Further, the metal board body of the printed board can positively dissipate heat transmitted to the pickup body of synthetic resin to the atmosphere. Therefore, the pickup body is neither thermally expanded nor deformed through heat generated by the laser diode but an optical axis connecting the photodiode and the objective lens with each other can be linearly maintained in a prescribed manner for preventing a reading error, similarly to a conventional metal pickup. 
   The board body of the printed board and the metal support substrate for the laser diode are brought into close contact with each other through the extension, whereby a heat dissipation area can be enlarged without increasing the size of the support substrate. Thus, a high-performance laser diode having high calorific power can also be used in a wide selection range, for manufacturing a high-performance optical pickup at a low cost. 
   According to a second aspect of the present invention, the optical pickup has a photodiode arranged in an opening formed on an end of a light transmission hole provided with a half mirror in a pickup body of synthetic resin, a collimator lens and an objective lens arranged in an opening formed on another end of the light transmission hole and a laser diode stored in the light transmission hole on a position opposed to the half mirror. A printed board connecting the photodiode and the laser diode to a connector through cables is provided on the outer peripheral surface of the pickup body. Such structure as described above is aimed at projecting a laser beam from the laser diode onto a disk through the half mirror, the collimator lens and the objective lens and receiving the laser beam reflected by the disk in the photodiode through the half mirror, thereby reading information recorded in the disk. In this optical pickup, a board body of the printed board consists of a metal plate, and at least a metal plate portion of the printed board corresponding to a connector pin portion fed with a high-frequency signal is notched. 
   In the metal plate forming the board body, at least the portion of the printed board corresponding to the connector pin portion fed with the high-frequency signal is notched as hereinabove described, to cause no electrostatic capacitance between the metal plate and the printed board. Therefore, the high-frequency signal can be prevented from a jitter, not to influence a tracking signal. 
   Further, the metal board body of the printed board can positively dissipate heat transmitted to the pickup body of synthetic resin to the atmosphere, whereby the pickup body is neither thermally expanded nor deformed through heat generated by the laser diode. Therefore, an optical axis connecting the photodiode and the objective lens with each other can be linearly maintained in a prescribed manner for preventing a reading error, similarly to a conventional metal pickup. 
   In the aforementioned optical pickup according to the second aspect of the present invention, the board body and a metal support substrate for the laser diode may be brought into contact with each other. 
   The board body of the printed board and the metal support substrate for the laser diode are brought into contact with each other through the extension as hereinabove described, whereby a heat dissipation area can be enlarged without increasing the size of the support substrate. Thus, a high-performance laser diode having high calorific power can also be used in a wide selection range. 
   In the aforementioned optical pickup according to the second aspect, an extension integrally provided on the metal support substrate for the laser diode may be inserted in a concave groove formed on the outer peripheral surface of the pickup body for fixing the board body to the pickup body thereby bringing the board body into close contact with the extension and the outer peripheral surface of the pickup body. 
   Thus, the board body of the printed board and the metal support plate for the laser diode are brought into close contact with each other through the extension, whereby the heat radiation area can be enlarged without increasing the size of the support substrate. Thus, a high-performance laser diode having high calorific power can also be used in a wide selection range. Further, the board body of the printed board is brought into close contact with the outer peripheral surface of the pickup body, thereby positively dissipating heat from the pickup body. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates the principle of an optical pickup to which the present invention is applied; 
       FIG. 2  is a perspective view of the optical pickup; 
       FIG. 3  is an exploded perspective view of the optical pickup; 
       FIG. 4  is a front elevational view of the optical pickup; 
       FIG. 5  is a plan view of the optical pickup; 
       FIG. 6  illustrates an optical pickup according to an embodiment of the present invention as viewed from a metal board body; 
       FIG. 7  illustrates a notch of the board body in detail; and 
       FIG. 8  is a schematic longitudinal sectional view of a conventional optical pickup. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates the principle of an optical pickup to which the present invention is applied. Referring to  FIG. 1 , a printed board  6  is mounted on a metal board body  6   a , which in turn is brought into contact with a metal support substrate  8  for a laser diode LD. The remaining structure of this optical pickup is identical to that shown in  FIG. 8 , and hence redundant description is not repeated. 
   As shown in  FIG. 2 , a pickup body  1 , made of hard synthetic resin, has a pair of brackets  1   b  and a rack  1   c  integrally projecting from a side surface of a base frame la substantially rectangular in plan view. Through holes  12  of the brackets  1   b  are movably engaged with a guide rod  13  for normally or reversely rotating a pinion (not shown) meshed with the rack  1   c  thereby moving the pickup body  1  in a direction “a” or “b” along the guide rod  13 . 
   A photodiode PD is arranged on the upper end of a main cylinder  1   d  integrally projecting from the upper portion of the base frame  1   a , while the laser diode LD is arranged on a branch cylinder  1   e  projecting from a side surface of the main cylinder  1   d.    
   The metal board body  6   a  of the printed board  6  consists of a metal plate such as a substantially rectangular aluminum plate as shown in  FIGS. 3 to 5 . A machine screw  7  is screwed into a screw hole  17  of the base frame  1   a  via a through hole  16  formed in a lower portion of the board body  6   a  thereby fixing the printed board  6  to the outer peripheral surface of the pickup body  1 . 
   According to this structure, the metal board body  6   a  positively dissipates heat transmitted to the pickup body  1  of synthetic resin to the atmosphere. Therefore, the pickup body  1  is neither thermally expanded nor deformed by heat generated by the laser diode LD. Consequently, an optical axis O connecting the photodiode PD with an objective lens OL can be linearly maintained in a prescribed manner for preventing a reading error similarly to the conventional metal pickup body  1 . Thus, a precision optical pickup can be manufactured at a low cost. 
   The metal support substrate  8  for the laser diode LD, formed by a metal plate of aluminum or the like bent in a U shape in plan view, consists of a central plate  8   a  fixed to an end surface of the branch cylinder  1   e  with a machine screw  18  and side plates  8   b  and  8   c  formed by bending both side edges of the central plate  8   a  toward the pickup body  1 . An extension  19  integrally extending from the first side plate  8   b  has a thickness t identical to or slightly larger than the depth d of a concave groove  20  formed on the side surface of the base frame  1   a  oppositely to the extension  19 . The extension  19  is inserted in the concave groove  20  for fixing the metal board body  6   a  to the side surface of the base frame  1   a,  thereby bringing the board body  6   a  into close contact with the extension  19  and the side surface of the base frame  1   a.    
   The metal board body  6   a  of the printed board  6  and the metal support substrate  8  for the laser diode LD are brought into close contact with each other through the extension  19  as hereinabove described, whereby a heat dissipation area can be enlarged without increasing the size of the metal support substrate  8 . Thus, the laser diode LD can be formed by a high-performance laser having high calorific power in a wide selection range. Further, the metal board body  6   a , brought into close contact with the side surface of the base frame  1   a , can positively dissipate heat from the pickup body  1 . 
   While the metal board body  6   a  can improve the heat dissipation effect as described above, electrostatic capacitance is caused between the metal board body  6   a  and the printed body  6  opposed to each other. 
   A connector  9  is mounted on the metal board body  6   a  for receiving an external driving signal for the laser diode LD and outputting a read signal from the photodiode PD through the connector  9 . The read signal from the photodiode PD is a high-frequency signal, the waveform of which is rounded due to the aforementioned electrostatic capacitance. This leads to a jitter influencing a tracking signal and deteriorating tracking performance. Thus, it may not be possible to read a signal from a disk. 
   An embodiment of the present invention implements an optical pickup ensuring a heat dissipation effect of a laser diode LD while causing no jitter in a read signal from a photodiode PD. 
     FIG. 6  illustrates the optical pickup according to the embodiment of the present invention as viewed from a metal board body  6   a , and  FIG. 7  illustrates a notch of the metal board body  6   a  in detail. 
   As shown in  FIGS. 6 and 7 , a printed board  6  is formed with terminal patterns  61  and wiring patterns  62  corresponding to connector pins  91  of a connector  9  supplied with read signals from the laser diode LD and the photodiode PD. A notch  6   b  is formed on a portion of the metal board body  6   a  corresponding to the wiring patterns  62  supplied with the read signal from the photodiode PD and the terminal patterns  61  corresponding to the connector pins  91 . 
   Referring to  FIG. 7 , the notch  6   b  of the metal board body  6   a  shows the pattern of the printed board  6  located under the same. The metal board body  6   a  can be prevented from forming electrostatic capacitance between the same and the terminal patterns  61  and the wiring patterns  62  due to the notch  6   b.    
   As shown in  FIG. 7 , the interval k between the terminal patterns  61  and the notch  6   b  is selected to at least exceed the thickness of the metal board body  6   a.    
   Referring to  FIG. 7 , the notch  6   b  is formed at least on the portion of the metal board body  6   a  corresponding to the terminal patterns  61  and the wiring patterns  62  of the connector pins  91  supplied with the read signal from the photodiode PD. Alternatively, a portion of the metal board body  6   a  corresponding to only the terminal pattern  61  of each connector pin  91  may be quadrangularly notched. In this case, the size of the notch of the metal board body  6   a  can be reduced for reducing deterioration of the heat dissipation effect. 
   Thus, the portion of the metal board body  6   a  corresponding to the terminal patterns  61  and the wiring patterns  62  corresponding to the connector pins  91  fed with a high-frequency signal is so notched that no electrostatic capacitance is caused between the metal board body  6   a  and the printed board  6 . Therefore, the optical pickup can prevent deterioration of an error rate while preventing the high-frequency signal from a jitter thereby preventing influence on a tracking signal. Thus, the optical pickup attains strong performance also as to a disk having side-runout, decentering or smudging. 
   Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.