Patent Publication Number: US-2005128894-A1

Title: Optical pickup actuator

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates, in general, to optical pickup actuators and, more particularly, to an optical pickup actuator, which improves the structures of a holder and a printed circuit board to which wires are fixedly attached, so that the wires can be soldered at exact locations, and so that gaps between magnets and coils can be adjusted through the adjustment of the positions of the wires, thus keeping the gaps uniform.  
      2. Description of the Related Art  
      Generally, an optical pickup is a device mounted on both a main shaft and a sub-shaft provided on a deck of an optical recording and reproducing apparatus to record signals on a variety of optical disks or reproduce the signals recorded on the optical disks while reciprocating along an axial direction. Typically, the optical pickup is divided into a pickup base and an actuator.  
      The pickup base is directly mounted on both the main shaft and the sub-shaft provided on the deck of the optical recording and reproducing apparatus, and reciprocates along the axial direction. In the pickup base, there are installed a laser diode for emitting light beams, a beam splitter for reflecting the light beams emitted from the laser diode in a direction of an optical disk, and a photodetector for receiving the light beams reflected from the optical disk and converting the light beams into electrical signals.  
      The actuator is movably installed on a top surface of the pickup base and functions to focus light beams on a single point on the optical disk through an object lens while moving together with the base.  
      For slim-type or portable-type optical recording and reproducing apparatuses, in the optical pickup actuators thereof, the central points of an object lens and a driving force do not coincide with each other due to the structural characteristics of the optical pickup actuators, so that defects due to subsidiary resonance frequently occur. Actually, because serious problems due to the subsidiary resonance defects occur at the time of production, measures to cope with the subsidiary resonance defects are required.  
      Properly, in order to solve the subsidiary resonance defects, several schemes, such as a magnetic attenuation apparatus or a mechanical attenuation apparatus, can be used. However, a scheme for adding gel between a wire holder and a printed circuit board to attenuate subsidiary resonance has been generally used.  
       FIGS. 1 and 2  illustrate an example of a conventional optical pickup actuator to which a scheme for adding gel to attenuate subsidiary resonance is applied.  
      Referring to  FIGS. 1 and 2 , in the conventional optical pickup actuator, a bobbin  20  provided with an object lens  22  is installed on a support plate  10  so that the position of the bobbin  20  can be finely adjusted in a focusing direction, that is, a vertical direction, and in a tracking direction, that is, a horizontal direction.  
      On a front portion of a top surface of the support plate  10 , a pair of opposite yokes  12 , spaced apart from each other by a predetermined distance, are formed to be extended upward. A pair of magnets,  14  which are permanent magnets, are symmetrically attached to opposite surfaces of the pair of yokes  12 .  
      Further, a wire holder  40  is fixedly mounted on a rear portion of the top surface of the support plate  10 , and a printed circuit board (PCB)  50  is closely attached to a rear surface of the wire holder  40 .  
      Tension parts  54  are formed in upper and lower portions of both ends of the PCB  50 , respectively. The tension parts  54  are made to be elastic by forming a plurality of notches  52  therethrough. Further, grooves are formed in the rear surface of the wire holder  40  at locations corresponding to those of the tension parts  54  of the PCB  50 . Gel  60  functioning as a damper is filled into spaces between the wire holder  40  and the tension parts  54  through the grooves so as to attenuate. subsidiary resonance.  
      The bobbin  20  has an approximately rectangular frame shape to have a central hollow portion. A tracking coil  24  is wound around the front portion of the bobbin  20  and a focusing coil  26  is wound around the side portion of the bobbin  20 .  
      Such a bobbin  20  is installed on the top surface of the support plate  10  to be finely movable through wires  30 .  
      That is, the wires  30  are connected to the upper and lower portions of both sides of the bobbin  20  through soldering. The wires  30  are horizontally extended to penetrate through the wire holder  40  and then fixed to the corresponding tension parts  54  of the PCB  50 , which is attached to the rear surface of the wire holder  40 , through soldering. Therefore, the bobbin  20  is elastically supported by a total of four wires  30  and, thus, it can be finely vertically or horizontally moved.  
      In this case, the bobbin  20  is installed so that the tracking coil  24  and the focusing coil  26  are located between the magnets  14  provided on the support plate  10 . At this time, it is important to keep gaps uniform between the magnets and the coils.  
      The operation of the conventional optical pickup actuator having the above construction is described in brief. If a current supplied to the PCB  50  is applied to the focusing coil  26  or the tracking coil  24  through the wires  30 , the object lens  22  is adjusted in the focusing or tracking direction while the bobbin  20  is moved by an electromagnetic force between the coil and the magnets  14  depending on the flow of the current.  
      The conventional optical pickup actuator, constructed and operated as described above, is problematic in that it is difficult to fix the wires to the tension parts of the PCB through soldering and to keep the gaps uniform between the magnets and the coils.  
      In order to describe the above problem in detail, a method of adjusting and fixing the positions of the wires is described with reference to  FIG. 3 .  
      When the conventional optical pickup actuator is assembled, one ends of the corresponding wires  30  are fixed to the upper and lower portions of the both sides of the bobbin  20  through soldering, and the other ends of the wires  30  are assembled to sequentially penetrate through the wire holder  40 , the gel  60  and the PCB  50 .  
      Thereafter, the position of the bobbin  20  is adjusted, so that the gaps between the coils placed on the bobbin  20  and the magnets  14  placed on the support plate  10  are kept uniform. After the position of the bobbin  20  is adjusted, the wires  30  are fixed to the tension parts  54  formed on the PCB  50  through soldering.  
      However, when a total of four wires are fixed to the corresponding tension parts of the PCB through soldering, the wires are not fixed at exact locations due to elasticity of the tension parts formed at the PCB but are vibrated, as represented by imaginary lines in  FIG. 3 .  
      Further, the conventional optical pickup actuator is problematic in that a case where the wires are not fixed at exact locations frequency occurs due to differences between the times required for solder applied on the four tension parts to solidify, in addition to the vibration of the tension parts at the time of soldering.  
      As described above, the conventional optical pickup actuator is problematic in that, as a total of four wires are fixed to the corresponding tension parts through soldering, a position error is generated, so that the position of the bobbin supported by the wires is changed and offset, thus varying the gaps between the coils and the magnets.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an optical pickup actuator, which prevents tension parts from being vibrated when wires are fixed to the tension parts of a PCB through soldering, thus enabling the wires to be fixed at the exact locations of the tension parts.  
      Another object of the present invention is to provide an optical pickup actuator, which can adjust the positions of the wires by varying the positions of the tension parts of the PCB after the wires are fixed to the tension parts of the PCB, thus keeping gaps uniform between coils and magnets.  
      A further object of the present invention is to provide an optical pickup actuator, which freely and precisely adjusts the gaps between the coils and the magnets, thus removing defects due to subsidiary resonance.  
      In order to accomplish the above object, the present invention provides an optical pickup actuator, comprising a support plate provided with a pair of yokes extended upward and a pair of magnets oppositely attached to opposite surfaces of the pair of yokes; a bobbin placed on a top surface of the support plate, and provided with an object lens located on a portion thereof and a tracking coil and a focusing coil wound on an outer side of the bobbin, the coils being installed to be located between the magnets; a wire holder fixed to a portion of the top surface of the support plate and provided with a depression formed in a center portion of a rear surface thereof to be depressed compared to both ends of the rear surface, the depression having a screw receiving hole formed in a center portion thereof; a printed circuit board closely attached to the rear surface of the wire holder and provided with a screw hole formed through a center portion thereof; a plurality of wires provided with first ends fixed to upper and lower portions of both sides of the bobbin and second ends extended from the first ends, the second ends penetrating through the wire holder and the printed circuit board and being fixed to a rear surface of the printed circuit board so as to elastically support the bobbin; a control screw engaged with the screw receiving hole of the wire holder after penetrating through the screw hole of the printed circuit board, the control screw allowing the printed circuit board to be arcuately bent while pressurizing a center portion of the printed circuit board to be located in the depression formed in the wire holder, thus deforming the printed circuit board to allow both ends thereof to be away from the wire holder; and gel functioning as a damper filled into spaces between the both ends of the arcuately bent printed circuit board and the wire holder.  
      In the optical pickup actuator, the wire holder may be provided with assembly bosses formed on opposite sides around the screw receiving hole in the rear surface of the wire holder to be protruded from the wire holder, and the printed circuit board may be provided with assembly holes formed therethrough at locations corresponding to those of the assembly bosses, the assembly holes being formed lengthwise in a transverse direction.  
      In the optical pickup actuator, the control screw may be designed so that a header part thereof pressurizes the printed circuit board and is then fixed to the printed circuit board through bonding or soldering so as to prevent the control screw from being disengaged after engagement of the control screw has been completed.  
      In the optical pickup actuator, the printed circuit board may be integrally provided with tension parts in upper and lower portions of the both ends of the printed circuit board to be made elastic by cutting away parts of the both ends thereof, and the wires may be fixedly attached to the corresponding tension parts.  
      Further, the present invention provides an optical pickup actuator, in which a bobbin provided with an object lens is elastically supported by a plurality of wires penetrating through a wire holder and being fixed to a printed circuit board, comprising a wire holder provided with a depression formed in a center portion of a rear surface thereof to be depressed compared to both ends of the rear surface, a printed circuit board closely attached to the rear surface of the wire holder, and provided with both ends to which corresponding wires are connected, and pressurizing means for allowing the printed circuit board to be arcuately bent while pressurizing a center portion of the printed circuit board to be located in the depression of the wire holder, the pressurizing means being fixed to the printed circuit board so as to maintain a bent state of the printed circuit board.  
      In the optical pickup actuator, the pressurizing means may be a control screw for pressurizing the printed circuit board through a header part thereof while penetrating through the printed circuit board and being engaged with the wire holder.  
      In the optical pickup actuator, the pressurizing means may comprise a control screw sequentially penetrating through the printed circuit board and the wire holder, and a nut engaged with the control screw on a front surface of the wire holder.  
      In the optical pickup actuator, the pressurizing means may comprises a control screw sequentially penetrating through the wire holder and the printed circuit board from a front surface of the wire holder, and a nut engaged with the control screw on a rear surface of the printed circuit board.  
      In the optical pickup actuator, the pressurizing means may be an adhesive for fixing parts of both the printed circuit board and the wire holder to each other to maintain a deformed printed circuit board after the printed circuit board is pressurized using a separate jig to be arcuately deformed.  
      The optical pickup actuator may further comprise gel functioning as a damper filled into spaces between the both ends of the arcuately bent printed circuit board and the wire holder.  
      In the optical pickup actuator, the printed circuit board may be integrally provided with tension parts in upper and lower portions of the both ends of the printed circuit board to be made elastic by cutting away parts of the both ends thereof, and the wires are fixedly attached to the corresponding tension parts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is an exploded perspective view of a conventional optical pickup actuator;  
       FIG. 2  is a top view of the conventional optical pickup actuator;  
       FIG. 3  is a view showing an assembly process to describe a conventional method of adjusting and fixing the positions of wires;  
       FIG. 4  is an exploded perspective view of an optical pickup actuator according to the present invention;  
       FIG. 5  is a top view showing the optical pickup actuator of the present invention;  
       FIG. 6  is a view showing an assembly process to describe a method of adjusting and fixing the positions of wires of the present invention;  
       FIG. 7  is a top view showing a means for pressing a PCB in the optical pickup actuator according to another embodiment of the present invention;  
       FIG. 8  is a top view showing a means for pressing a PCB in the optical pickup actuator according to a further embodiment of the present invention; and  
       FIG. 9  is a top view showing a means for pressing a PCB in the optical pickup actuator according to still another embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.  
      Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.  
       FIG. 4  is an exploded perspective view of an optical pickup actuator according to the present invention,  FIG. 5  is a top view showing the optical pickup actuator of the present invention, and  FIG. 6  is a view showing an assembly process to describe a method of adjusting and fixing the positions of wires of the present invention.  
      Referring to FIGS.  4  to  6 , in the optical pickup actuator of the present invention, a bobbin  20  provided with an object lens  22  is installed on a support plate  10  so that the position of the bobbin  20  can be finely adjusted in a focusing direction, that is, a vertical direction, and in a tracking direction, that is, a horizontal direction.  
      On a front portion of a top surface of the support plate  10 , a pair of opposite yokes  12 , spaced apart from each other by a predetermined distance, are formed to be extended upward. A pair of magnets,  14  which are permanent magnets, are symmetrically attached to opposite surfaces of the pair of yokes  12 .  
      The bobbin  20  has an approximately rectangular frame shape to have a central hollow portion. A tracking coil  24  is wound around the front portion of the bobbin  20  and a focusing coil  26  is wound around the side portion of the bobbin  20 .  
      Further, the bobbin  20  is installed on the top surface of the support plate  10  to be finely movable through a plurality of wires  30 . In this case, the bobbin  20  is installed so that winding parts of the tracking coil  24  and the focusing coil  26  are located between the magnets  14  provided on the support plate  10 . At this time, gaps between the magnets and the coils should be kept uniform.  
      A method of elastically supporting the bobbin  20  by the wires  30  is described in detail. The wires  30  are connected to the upper and lower portions of both sides of the bobbin  20  through soldering. The Extended parts of the wires  30  penetrate through a wire holder  100  and are then fixed to a printed circuit board (PCB)  200  through soldering.  
      In this way, the bobbin  20  is elastically supported to be finely movable by a total of four wires  30 . Further, if the positions of the wires  30  are adjusted forward or backward, the position of the bobbin  20  is also changed forward or backward.  
      The wire holder  100  is fixedly mounted on the top surface of the support plate  10 .  
      Further, wire passing holes  110  are formed in upper and lower portions of both sides of the wire holder  100  to allow the wires  30  to penetrate therethrough. A depression  120  is formed in a center portion of a rear surface of the wire holder  100  to be depressed inward compared to both ends of the wire holder  100 . Further, a screw receiving hole  130  is formed in a center portion of the depression  120 . Assembly bosses  140  are formed on both side edges of the depression  120  to be protruded backward.  
      The PCB  200  is closely attached to the rear surface of the wire holder  100 .  
      A screw hole  210  is formed through a center portion of the PCB  200  corresponding to that of the screw receiving hole  130  of the wire holder  100  to allow a control screw, which will be described later, to be engaged with the screw hole  210 . Further, assembly holes  220  are formed on the opposite sides around the screw hole  210  of the PCB  200  at locations corresponding to those of the assembly bosses  140  of the wire holder  100 . At this time, the assembly holes  220  are preferably formed lengthwise in a transverse direction of the PCB so that the PCB  200  is movable along the assembly bosses  140 .  
      Further, tension parts  240  are integrally formed in upper and lower portions of both ends of the PCB  200 , wherein the tension parts  240  are made to be elastic by the action of a plurality of notches  230  formed by cutting away parts of the both ends of the PCB  200 . Wire holes  242  into which the wires  30  are inserted are formed through the PCB  200  at locations of the tension parts  240  corresponding to those of the wire passing holes  110  of the wire holder  100 .  
      According to the present invention, the control screw  300  is assembled so that it penetrates through the screw hole  210  of the PCB  200  and is then engaged with the screw receiving hole  130  of the wire holder  100 .  
      When the control screw  300  is engaged with the screw receiving hole  130 , a header part thereof pressurizes the PCB  20 , so that the center portion of the PCB  200  is bent toward the depression  120  of the wire holder  100  and located in the depression  120  due to the pressure. Then, as the PCB  200  is arcuately bent, both ends thereof are bent to be away from the wire holder  100 .  
      Therefore, in the present invention, the levels of bending of the PCB  200  differ depending on a length by which the control screw  300  is engaged. As the bending level is high, the wires  30  fixed to the tension parts  240  of the PCB  200  are gradually strained backward, and the bobbin  20  is moved backward in proportion to the strain of the wires  30 . Therefore, it is possible to adjust the gaps between the coils of the bobbin  20  and the magnets  14  of the support plate  10 . Properly, it is preferable to control the bending level of the PCB  200  at a location where the gaps between the coils and the magnets are kept uniform.  
      In this case, it is preferable that, after the engagement of the control screw  300  has been completed, the header part of the control screw  300  is fixed to the PCB  200  through bonding or soldering so as to prevent the disengagement of the control screw  300 .  
      According to the present invention, spaces between both ends of the PCB  200  arcuately bent and the wire holder  100  are filled with typical gel  60  functioning as a damper.  
      The assembly of the optical pickup actuator of the present invention having the above construction is described below.  
      First, a total of four wires  30  are connected to the upper and lower portions of both sides of the bobbin  20 , respectively, through soldering.  
      Further, the wire holder  100  is fixed to the top surface of the support plate  10 , and then the PCB  200  is attached to the rear surface of the wire holder  100 . That is, the PCB  200  is closely attached to the rear surface of the wire holder  100  so that the assembly bosses  140  formed on the rear surface of the wire holder  100  are inserted into the assembly holes  220  formed in the PCB  200 . Thereafter, the control screw  300  penetrates through the screw hole  210  of the PCB  200  and is then engaged with the screw receiving hole  130  formed in the wire holder  100 . At this time, the control screw  300  is engaged until it pressurizes the PCB  200 .  
      Thereafter, the extended parts of the wires  30  connected to the bobbin  20  penetrate through the wire holder  100  and are then fixed to the corresponding tension parts  240  of the PCB  200  through soldering. At this time, the bobbin  20  is installed so that the tracking coil  24  and the focusing coil  26  of the bobbin  20  are located between the pair of magnets  14  provided on the support plate  10 .  
      Then, as shown in  FIG. 6 , the PCB  200  is allowed to be arcuately bent while the control screw  300  is slowly tightened, so that the wires  30  fixed to both ends of the PCB  200 , that is, the tension parts  240 , are strained backward. Therefore, the bobbin  20  is moved backward together with the wires  30 . Properly, if the bobbin  20  is moved and then the gaps between the tracking or focusing coil and the magnets  14  of the support plate  10  are kept uniform, an operation of tightening the control screw  300  needs to be stopped.  
      After the adjustment of the position of the bobbin  20  has been completed, spaces between the wire holder  100  and the tension parts  240  of the PCB  200  are filled with the gel  60  functioning as a damper. After all operations have been completed, the header part of the control screw  300  is finally fixed to the PCB  200  through soldering or bonding.  
      The driving of the optical pickup actuator of the present invention constructed and assembled as described above is described below in brief.  
      The optical pickup actuator of the present invention is driven so that, when a current supplied to the PCB  200  is applied to the focusing coil  26  or the tracking coil  24  through the wires  30 , the object lens  22  is finely adjusted in the focusing or tracking direction while the bobbin  20  is moved by an electromagnetic force between the coil and the magnets  14  depending on the flow of the current.  
      The optical pickup actuator of the present invention constructed and operated as described above has a plurality of advantages.  
      First, the present invention is advantageous in that, when the wires connected to the bobbin are fixed to the corresponding tension parts of the PCB through soldering, the tension parts are not moved while being fully attached to the rear surface of the wire holder, thus enabling a soldering operation to be performed at exact locations.  
      Further, the present invention is advantageous in that the wires are first fixed to the PCB through soldering and then strained while the control screw is tightened, so that the position of the bobbin is adjusted, thus keeping the gaps uniform between the tracking or focusing coil placed on the bobbin and the magnets placed on the support plate.  
      Further, the present invention is advantageous in that, when the positions of the gaps are erroneously changed and the gaps are irregularly arranged during assembly, the positions of the gaps can be readjusted by changing the position of the bobbin while loosening and tightening the control screw again.  
      Moreover, the present invention is advantageous in that, when subsidiary resonance is measured after the gel is filled into spaces between the wire holder and the PCB, a distance between the wire holder and the PCB is adjusted and thus the position of the bobbin can be finely adjusted, so that the amount of subsidiary resonance is adjusted to a suitable level or less. Therefore, most defects occurring due to subsidiary resonance can be repaired.  
      In the meantime, the embodiment of the present invention is constructed so that the center portion of the PCB is pressurized using the control screw and then the PCB is bent arcuately. However, this construction is only an embodiment of the present invention. Any schemes provided with a pressurizing means capable of pressurizing the center portion of the PCB to arcuately deform the PCB and maintain the deformed PCB can be freely applied to the present invention.  
      FIGS.  7  to  9  are views showing a means for pressurizing the PCB according to other embodiments of the present invention. Only differences between the above embodiment and other embodiments are described below.  
      Referring to  FIG. 7 , the means for pressurizing the PCB applicable to the present invention is constructed in such a way that a control screw  300 - 1  sequentially penetrates the PCB  200  and the wire holder  100  from the rear surface of the PCB  200 , and a nut  310  is engaged with the control screw  300 - 1  on the front surface of the wire holder  100 , so that the control screw  300 - 1  can pressurize the PCB  200  while loosening and tightening the nut  310  on the control screw  300 - 1 .  
      The pressurizing means can be constructed so that, after the nut  310  is first fixed to the wire holder  100  through soldering or bonding, the control screw  300 - 1  having sequentially penetrated through the PCB  200  and the wire holder  100  is engaged with the nut  310 , and pressurizes the PCB  200  while loosening and tightening the control screw  300 - 1 .  
      After the engagement of the screw with the nut has been completed, the header part of the screw  300 - 1  needs to be fixed to the PCB  200  through bonding or soldering so as to prevent the disengagement of the screw.  
      Next, referring to  FIG. 8 , the PCB pressurizing means applicable to the present invention is constructed in such a way that the control screw  300 - 1  sequentially penetrates through the wire holder  100  and the PCB  200  from the front surface of the wire holder  100 , and the nut  310  is engaged with the control screw  300 - 1  on the rear surface of the PCB  200 , so that the control screw  300 - 1  can pressurize the PCB  200  while loosening and tightening the nut  310  on the control screw  300 - 1 .  
      The pressurizing means can be constructed so that, after the nut  310  is first fixed to the PCB  200  through soldering or bonding, the control screw  300 - 1  having sequentially penetrated through the wire holder  100  and the PCB  200  is engaged with the nut  310  and pressurizes the PCB  200  while loosening and tightening the control screw  300 - 1 .  
      After the engagement of the screw with the nut has been completed, the header part of the screw  300 - 1  needs to be fixed to the wire holder  100  through bonding or soldering so as to prevent the disengagement of the screw.  
      Next, referring to  FIG. 9 , the PCB pressurizing means applicable to the present invention can be constructed so that parts of both the PCB  200  and the wire holder  100  are fixed to each other using an adhesive  300 - 2 , such as a bond, while the PCB  200  is bent after the PCB  200  is pressurized using a separate jig (not shown).  
      Although not shown in detail, for the PCB pressurizing means applicable to the present invention, an operating principle of a typical nipple can be employed, in addition to the above-described embodiments.  
      Further, the optical pickup actuator of the present invention can be applied to all types of optical pickup units and optical recording and reproducing apparatuses.  
      As described above, the present invention provides an optical pickup actuator, in which wires are soldered after tension parts of a PCB are fixed to be unable to move, so that the wires can be soldered and fixed to exact locations.  
      Further, the present invention is advantageous in that, since the wires are first fixed and then the PCB is deformed to precisely adjust the position of a bobbin while the wires are strained or released, gaps between coils provided on the bobbin and magnets provided on a support plate can be precisely adjusted, thus keeping the gaps optimum.  
      Further, the present invention is advantageous in that, since then the position of the bobbin is precisely adjusted when subsidiary resonance is measured after gel is filled, the amount of subsidiary resonance can be adjusted to a suitable level or less, thus enabling most defects occurring due to subsidiary resonance to be repaired.  
      Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.